QUALITY OF HEAT PHYSICS REVISION

QUALITY OF HEAT

1. (a) Define the term specific heat capacity.

(b) A block of metal of mass 300g at 100⁰c is dropped into a logged calorimeter of heat capacity 40Jk^-1, containing 200g of water at 20⁰c. The temperature of the resulting mixture is 34⁰c. (Specific heat capacity of water = 4200Jkg^-1k^-1)

Determine:

(i) Heat gained by calorimeter.

(ii) Heat gained by water.

(iii) Heat lost by the metal block.

(iv) Specific heat capacity of the metal block.

2. (a) State two differences between boiling and evaporation.

(b) 200g of a solid was uniformly heated by a 0.2 kw heater for sometime. The graph in the figure below shows how the temperature of the solid changed with time.

(i) Explain what is happening between OA and AB.

(ii) Calculate the specific heat capacity of the solid.

(iii) Calculate the specific latent heat of fusion k of the solid.

3. (a) Define the term heat capacity
4. b) A block of metal of mass 150g at 100^oC is dropped into a logged calorimeter of heat capacity 40Jk^-1 containing 100g of water at 25^o The temperature of the resulting mixture is 34^oC. (Specific heat capacity of water = 4200J/KgK)

Determine;-

(i) Heat gained by calorimeter

(ii) Heat gained by water

(iii) Heat lost by the metal block

(iv) Specific heat capacity of the metal block

4. (a) Distinguish between evaporation and boiling

(b) A jet delivering 0.44g of dry steam per second, at 100^oC is directed on to crushed ice at 0.0^oC contained in an unlagged copper can which has a hole in the base. 4.44g of water at 0.0^oC flow out of the hole per second

• How many joules of heat are given out per second by condensing steam and cooling to 0.0^oC of water formed?(Latent heat of vaporization of steam = 2.26 x 10⁶JKg^-1, c for water = 4200JKg^-1K^-1)
• How much heat is taken in per second by the ice which melts?
• Suggest why these amounts above are different

(c) Figure 7 below shows a cross-section of a vacuum flask

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(i) Name the parts labelled A and B on the diagram

(ii) Explain how the heat losses are minimized when hot liquid is poured into the flask

5. (a) Figure 2 shows two identical thermometers. Thermometer A has a blackened bulb while thermometer B has a silvery bulb. A candle is placed equidistant between the two thermometers

State with a reason the observations made after some time

(b) Figure 3 shows a test tube partially filled with water. An ice wrapped in wire gauze is

placed at the bottom of the test-tube. It is then held in the flame of a bunsen burner as

shown below

fig. 3

State and explain what will be observed after some time

6. Give any two differences between evaporation and boiling
7. Explain why steel feels colder than wood at the same temperature

8. An electric heater 1KW 240V is used to raise the temperature of a 5kg copper block from 15^oC to 33^o If the specific heat capacity of copper is 400JKg^-1K^-1 and assuming no heat is lost to the surrounding,

Calculate the time taken

9. (a) Define specific latent heat of fusion

(b) 0.5kg of naphthalene contained in an aluminium can of mass 0.4kg is melted in a water bath and raised to a temperature of 100^oC. Calculate the total heat given out when the can and its contents are allowed to cool to room temperature, 20^oC. Neglect losses by          evaporation during heating process  and give your answer to the nearest kilojoule.

           (For naphthalene melting point = 80^oC , Specific heat  capacity for both liquid and 

             solid =2100J/KgK; specific latent heat of fusion = 170000J/Kg.

             For aluminium: specific heat capacity = 900J/Kgk                                                            

(c) Briefly explain two ways other than direct heating by which quantity of liquid may be made to evaporate more quickly

(d) The diagram below shows a charcoal refrigerator

(i) Explain why charcoal is used and why it is sprinkled with water

(ii) What is the role of the metallic tank and the wire mesh

10. An electric kettle with a shinny outer surface would be more efficient than one with a dull outer surface. Give a reason for this
11. A heating element rated 2.5 KM is used to raise the temperature of 3.0 kg of water through 50oC. Calculate the time required to Effect this. (Specific heat capacity of water is 4200J/kgK).
12. An electric heater rated 6000W is used to heat 1kg of ice initially at -10⁰c until all the mass turns to steam. Given that

Latent heat of fusion =334kJ^-1

Specific heat capacity of ice= 2,260J kg ^-1 K ^-1

Specific heat capacity of water = 4, 200J kg^-1 K^-1

Latent heat of vaporization = 2, 260KJ kg ^-1 K ^-1

Calculate the minimum time required for this activity.

13. a) Explain why a burn from the steam of boiling water more severe that of water itself?
14. b) An energy saving stove when burning steadily has an efficiency of 60%. The stove melts 0.03kg of ice at 0⁰c in 180 seconds.

Calculate; –

1. i) The power rating of the stove.
2. ii) The heat energy wasted by the stove.
3. c) A pump uses a mixture of petrol and alcohol in the ratio 4: 1 by mass to raise 100kg of water from a well 200m deep.
4. i) How much energy is given by 1g of mixture?
5. ii) If the pump is 40% efficient, what mass of this mixture is needed to raise the water?
6. d) i) Suggest two energy changes that accompany the changing

of a liquid in a vapour phase.

1. ii) Explain why the time calculated in (i) above is minimum
2. An immersion heater rated 90W is placed in a liquid of mass 2kg. When the heater is switched on for 15 minutes, the temperature of the liquid rises from 20⁰C to 30⁰ Determine the specific heat of the liquid.
3. State two factors that would raise the boiling point of water to above 100⁰c
4. a) State what is meant by the term specific latent heat of vaporization
5. b) In an experiment to determine the specific latent heat of vaporization of water, steam at 100⁰c was passed into water contained in a well-lagged copper calorimeter. The following measurements were made:

Mass of calorimeter   = 50g

Initial mass of water   = 70g

Final mass of calorimeter + water + condensed steam = 123g

Final temperature of mixture = 30⁰C

(Specific heat capacity of water = 4200 J kg ^-1K and specific heat capacity for copper = 390 J kg ^-1 K^-1)

Determine the

1. i) Mass of condensed steam
2. ii) Heat gained by the calorimeter and water

iii)       Given that L is the specific latent heat of evaporation of steam

1. Write an expression for the heat given out by steam
2. Determine the value of L.
3. A heating element rated 2.5 KW is used to raise the temperature of 3.0 kg of water through 50⁰ Calculate the time required to effect this.  (Specific heat capacity of water is 4200 J/kgK)
4. An electric heater is connected to the mains supply. A fault in the mains reduces the supply potential slightly. Explain the effect on the rate of heating of the heater.
5. In an experiment to determine the power of an electric heater, melting ice was placed in a container with an outlet and the heater placed in the ice as shown in Fig. 2. The heater was connected to a power supply and switched on for some time. The melted ice was collected.

1. a) Other than the current and voltage, state the measurement that would be taken to determine the quantity of heat absorbed by the melted ice in unit time.
2. b) If the latent heat of fusion of ice is L, show how measurements in (i) above would be used in determining the power P, of the heater, (2mks)
3. c) It is found that the power determined in this experiment is lower than the manufacturer’s value indicated on the heater.                    (1mk)
4. Fig 11 shows the variation of temperature ‘q’ with time t, when an immersion heater is used to heat a certain liquid. Study the figure and answer questions below

1. State the reason for the shape of the graph in the section labelled BC.
2. Sketch on the same axes the graph for another liquid of the same mass but higher specific heat capacity when heated from the same temperature.
3. State two factors that affect the melting point of ice.
4. a) Define the term specific latent heat of vaporization of a substance.
5. b) Figure 11 shows the features of domestic refrigerators. A volatile liquid circulates the capillary tubes under the action of the compression pump.

(i)              State the reason for using a volatile liquid.

(ii)             Explain how the volatile liquid is made to vaporize in the cooling compartment and to condense in the cooling fins.

(iii)                        Explain how cooling takes place in the refrigerator.

(iv)                        What is the purpose of the double wall?

3. c) Steam of mass 3.0g at 100⁰c is passes into water of mass 400g at 10⁰ The final temperature of the mixture is T. The container absorbs negligible heat. (Specific latent heat of vaporization of steam= 2260 kJ/kg, specific heat capacity of water= 4200Jk^-1)
4. i) Derive an expression for the heat lost by the steam as it condenses to water at temperature T.
5. ii) Derive an expression for the heat gained by the water.

iii) Determine the value of T.

23. A can together with stirrer of total head capacity 60j/k contains 200g of water at 10⁰ dry steam at 100⁰c is passed in while the water is stirred until the whole reaches a temperature of 30⁰c Calculate the mass of steam condensed.
24. An immersion heater which takes a current of 3A from 240V mains raised the temperature of 10kg of water 30⁰c to 50⁰ How long did it take?
25. 100g of boiling water are poured into a metal vessel weighing 800g at a temperature of 20⁰c if the final temperature is 50⁰ What is the specific heat capacity of the metal? (Specific Heat capacity of water 4.2 x 10³J/kgk)
26. 02kg of ice and 0.01kg of water 0⁰c are in a container. Steam at 100⁰c is passed in until all the ice is just melted.  How much water is now in the container?
27. In a domestic oil-fired boiler, 0.5kg of water flows through the boiler every second. The water enters the boiler at a temperature of 30⁰c and leaves at a temperature of 70⁰c, re-entering the boilers after flowing around the radiators at 30⁰  3.0x 10⁷J of heat is given to the water by each kilogram of oil burnt.  The specific heat capacity of water is 4200Jkg ^-1K^-1

Use the information above to calculate the energy absorbed by the water every second as it passes through the boiler

Use the same information above to calculate the mass of oil which would need to be burnt in order to provide this energy.

28. You are provided with two beakers. The first beaker contains hot water at 70⁰  The second beaker contains cold water at 20⁰c.  The mass of hot water is thrice that of cold water.  The contents of both beakers are mixed.  What is the temperature of the mixture?
29. Calculate the heat evolved when 100g of copper are cooled from 90⁰c to 10⁰ (Specific Heat Capacity of Copper = 390J/Kgk).
30. An-immersion heater rated 150w is placed in a liquid of mass 5 kg. When the heater is switched on for 25 minutes, the temperature of the liquid rises from 20 – 270⁰  Determine the specific heat capacity of the liquid.  (Assume no heat losses)
31. Njoroge wanted to determine the heat energy, W, required to change one kilogram of water into vapour at a constant temperature. He set up the arrangement as shown below;

He took the reading M, of the balance at a given time interval. He obtained the following data

(a) Plot a graph of mass against time

• Determine the gradient of the graph
• What does the gradient represent?
• A steady current of 4A and potential difference of 12V were recorded during the experiment. Determine the value of W .

32. (a) You are provided with the following apparatus:

A filter funnel, a thermometer, a stop watch, ice at 0°C, an immersion heater rated P watts, a beaker, a stand, boss and clamp and a weighing machine.

Describe an experiment to determine the specific latent heat of fusion of ice. Clearly state the measurements to be made.

(b) 200 g of ice at 0°C is added to 400g water in a well lagged calorimeter of mass 40g. The initial temperature of the water was 40°C. If the final temperature of the mixture is X°C, (Specific latent of fusion of ice L = 3.36 x 10⁵ Jkg^-1, specific heat capacity of water, c = 4200Jkg^-1K^-1, specific heat capacity of copper = 400 Jkg^-1K^-1.)

(i) Derive an expression for the amount of heat gained by ice to melt it and raise its temperature to X°C

(ii) Derive an expression for the amount of heat lost by the calorimeter and its content when their temperature falls to X°C.

(iii)     Determine the value of X.

(c) A hydrogen balloon of volume 1.2 m³ is released at the ground level where the pressure is 680 mmHg and a temperature of 20 °C. Determine the volume of the balloon at a height of 2500m above the ground where the pressure drops to 500 mmHg and the temperature is 4°C.

33. a) State the two factors that affect the boiling point of water and in each case, explain how the boiling is affected.
34. b) Distinguish between evaporation and boiling
35. c) A copper block of mass 800g is suspended in a freezing mixture -60⁰C for some time and then transferred to a large volume of water at 0⁰ A layer of ice is formed on the block. Take specific heat capacity of copper =360JKg^-1K^-1, latent heat of fusion 336,000JKg^-1

• Give a reason for the formation of ice
• State the temperature of the copper block after this change is complete
• Determine the mass of ice formed

34. (a) Define specific latent heat of fusion of a substance

(b)       Water of mass 400g at a temperature of 60^oC is put in a well lagged copper calorimeter of mass 160g. A piece of ice at 0^oC and mass 40g is placed in the calorimeter and the mixture stirred gently until all the ice melts. The final temperature, T, of the mixture is then measured. Determine;

• The heat absorbed by the melting ice at 0^oC
• The heat absorbed by the melted ice (water) to rise the temperature T (Answer may be given in terms of T)
• The heat lost by the warm water and the calorimeter (The answer may be given in terms of T)
• The final temperature T of the mixture (Specific latent heat of fusion of ice = 334000J/kg, specific heat capacity of water = 4200J/kgK, specific heat capacity of copper = 900J/kgK)

35. (a) Differentiate between heat capacity and Specific heat capacity of a substance

(b) Briefly describe an experiment to determine the specific heat capacity of a liquid                          substance using the electrical method.

(c)       An immersion heater rated 1000W is used to heat a block of ice of mass 500g initially at -10°C until the all the water evaporates at 95°C. Assuming that all the heat supplied is      used to heat the ice, calculate the time in minutes for the whole process to take place. (Take        specific heat capacity of water as 4200J/KgK, specfic heat capacity of ice = 2100J/Kg K specific latent heat of fusion = 3.35 x 10⁵ J/Kg and specific latent heat of vapourization 2.26 x 10⁵J/Kg)

36. (a) What is meant by specific latent heat of Vaporization?
37. b) In an experiment to determine the specific latent heat of vaporization of water, steam at 100^oc was passed into water contained in a well lagged copper calorimeter.

The following measurements were made:

Mass of calorimeter = 50g

Initial mass of water = 70g

Initial temperature of water = 5^oc

Final mass of water + Calorimeter + condensed steam = 123g

Final temperature of mixture = 30^oc

Specific heat capacity of water = 4200jkg^-1k^-1

Specific heat capacity of copper = 390k kg^-1k^-1

• Determine the

(i)Mass of condensed steam

(ii)Heat gained by water and calorimeter

(ii) Given that L is the specific latent heat of vaporization of steam

(i) Write an expression for the heat given out by steam

(ii)Determine the value of L

1. 500g of water at 20^oc is mixed with 200g of water at 55^o Find the final temperature of the mixture.
2. (a) Distinguish between heat and temperature

(b) Define specific heat capacity

(c) The figure below shows a graph of temperature against time for a given substance (water)

State what happens in the section labelled

• BC
• CD
• DE

(d) A hot-water tank for a house contains 150kg of water at 15⁰C. the tank itself has a heat capacity of 6000 JK^-1. an immersion heater is used to heat the water to 50⁰c. the tank is well insulated and the power of the heater is 2500W (specific heat capacity of water =4200 JKg^-1K^-1

• Find the amount of heat transferred to the water
• find how much heat is absorbed by the tank
• Determine the time it will take the heater to raise temperature to 50⁰

38. a)    Define specific latent heat of fusion of a substance
39. A mass is receiving heat at the rate  per minutes and its temperature at various times recorded as follows

• Plot a graph of temperature against time on the grid provided
• Use your graph to find
  • The specific heat capacity of the substance in its liquid state
  • Its boiling point
  • Its melting point
  • The specific latent heat of fusion of the substances

39. (a) Define specific latent heat of vaporization.

(b) In an experiment to determine the specific latent heat of vaporization of water,

steam at 100⁰C was passed into water contained in a well lagged copper calorimeter.

The following measurements were made

Mass of calorimeter = 50g

Initial mass of water = 70g

Initial temperature of water = 5⁰C

Final mass of calorimeter + water + condensed steam = 123g

Final temperature of mixture = 30⁰C

Specific heat capacity of water is 4200JKg^-1k^-1 and specific heat capacity of copper is 390JKg^-1k^-1 )

(I) Determine the:-

(i) Mass of condensed steam.

(ii) Heat gained by the calorimeter and water.

(II) Given that L is the specific latent heat of vaporization of steam.

(i) Write an expression for the heat given out by the steam.

(ii) Determine the value of L.

40. (a) Define specific latent heat of fusion of a substance

(b) Water of mass 200g at a temperature of 60^oC is put in a well lagged copper calorimeter of mass 80g. A piece of ice at 0^oC and mass 20g is placed in the calorimeter and the mixture stirred gently until all the ice melts. The final temperature of the mixture is then measured

(Latent heat of fusion of ice = 33400Jkg^-1, specific heat capacity of water  = 4200Jkg^-1K^-1)

Determine:

• The heat absorbed by the melting ice at 0^oC
• The heat absorbed by the melted ice (water ) to rise to temperature T
• The heat lost by the warm water and the calorimeter (Specific heat capacity of the calorimeter = 900Jkg^‑1K^-1)
• The final temperature T of the mixture

41. a) Ether is put into a beaker which is placed on a thin film of water. A student blows the ether through a pipe continuously.  State and explain the observation made after some time
42. b) The rate of evaporation can be increased in a number of ways. State two ways in which this could be achieved
43. c) Differentiate between specific heat capacity and heat capacity
44. d) An electric kettle rated at 2.5kw contains 1.6kg of water.  It is left switched on after boiling.How much heat energy will be used in turning all the water to steam?
45. e) Determine how long will it take for the 2.5kw kettle to boil dry
46. (a) Distinguish between heat capacity and specific heat capacity of a substance.
47. b) The figure below represent a set up used to determine the specific latent heat vaporization of water by electrical method.

(i)        State the measurements to be taken in order to achieve the aim of the experiment.

(ii)      State the conclusion from the observations made in the figure b(i) above.

1. c) Why is the latent heat of fussion of water of lower value than latent heat of vaporization of the same water.

II a)     Why are the elements of domestic heating appliances made of nichrome

wire instead of tangsten wire.

1. b) What property does a fuse wire have that make it suitable for controlling excessive currents in circuits.
2. c) What do you understand by rating 150w, 240v indicated on an electric bulb?
3. a) Define specific heat capacity
4. b) State two factors that would raise the boiling point of water
5. c) In a cooling system 100g of steam at 100⁰C was passed into cold water at 40⁰ The temperature rose to 70⁰C (specific heat capacity of water = 4200J kg^-1K^-1, latent heat of vaporization of steam = 2.2 x 106Jkg^-1)

Calculate

1. i) Heat lost by steam
2. ii) Heat lost by condensed steam

iii)       The mass of cold water used

44. (a) Define the term specific heat of vaporization.

(b) The setup shown below was used to determine the specific latent heat of vapourisation of water.

Describe how you would use the apparatus to determine the specific latent heat of vapourisation of water stating any assumption made and the measurements one would take.

(c) 50g of steam at 100^oC was passed into cold water at 20^oC.  The temperature on the water rose to 60^oC.  Determine the mass of cold water used (specific heat capacity of water = 4200J/KgK and specific latent heat of vapourisation of water = 2.26 x 10⁶ JKg-1)

45. a) Define specific latent heat of vaporization of a substance
46. b) Explain why food cooks faster in a pressure cooker than in an open sufuria
47. c) 32g of dry ice was added to 200g of water at 25⁰C in a beaker of negligible heat capacity. When all ice had melted, the temperature of water was found to be 10⁰ (Take specific heat capacity of water to be 4200JKg^-1K^-1)
48. i) Calculate the heat lost by water
49. ii) Write an expression for total heat gained by ice to melt and for temperature to rise to 10⁰C

iii)       Calculate the specific latent heat of fusion of ice

46. (a) What is meant by specific latent heat of Vaporization?

(b) In an experiment to determine the specific latent heat of vaporization of water, steam at 100°c was passed into water contained in a well lagged copper calorimeter.

The following measurements were made:

Mass of calorimeter = 50g

Initial mass of water =70g

Initial temperature of water = 5°c

Final mass of water + Calorimeter + condensed steam =123g

Final temperature of mixture =30°c

Specific heat capacity of water = 4200Jkg^-1k^-1

Specific heat capacity of copper =390J kg^-1k^-1

(a) Determine the

(i)Mass of condensed steam

(ii)Heat gained by water and calorimeter.

(b) Given that L is the specific latent heat of vaporization of steam

(i) Write an expression for the heat given out by steam.

(ii)Determine the value of L

1. c) 500g of water at 20°c is mixed with 200g of water at 55^oC Find the final temperature

of the mixture.

47. a) Define latent heat of vaporization.
48. b) Figure 11 shows a set up by a student to determine the specific latent heat of vaporization of a liquid.

Fig. 11

1. Identify the parts labelled X and Y
2. State the measurements that should be taken.

• Describe how the set up can be used to determine the specific latent heat of vaporisation of the liquid.

1. What is the purpose of the condenser?
2. a) Define specific heat capacity.
3. b) State two feature which makes a liquid-in-glass thermometer sensitive.    c) In an experiment to determine the specific heat capacity of paraffin 2.0 kg of paraffin was supplied with 21600 J of heat and its temperature rose by 4.9^oC calculate the specific heat capacity of paraffin.                                                                                                                d) Boiling water is poured into two identical vacuum flasks A and B. Flask A is partially filled while flask B is completely filled. Both are closed tightly. State with reason the flask in which the water is likely too have a higher temperature eight hours later.
4. e) A block of ice of mass 40g at 0oC is placed in a calometer containing 400g of water at 20^o Ignoring the heat absorbed by the calorimeter. Determine the final temperature of the mixture after all the ice has melted.

Specific heat capacity of water = 4200 J Kg^-1K^-1

Specific latent heat of fusion of ice = 340,000 Jkg^-1

49. A liquid at 80°C in a cup was allowed to cool for 20 minutes. State two factors that determine the final temperature.
    • What is meant by specific latent heat of vaporization?
    • In an experiment to determine the specific latent heat of vaporization L of water, steam at 100°C was passed into water contained in a well legged copper calorimeter. The following measurements were made.

Mass of calorimeter = 80g

Initial mass of water = 70g

Initial temperature of water = 5°C

Final mass of calorimeter + water +condensed steam = I 56g

Final temperature of mixture = 30°C

Specific heat capacity of water = 4200JKg^-1K^-1and specific heat capacity for copper = 390J/Kg^-1K^-1)

(i) Determine the:

(I) Mass of condensed steam

(II) Heat gained by the calorimeter and water

(ii) Given that L. is the specific latent heat of vaporization of steam

(I) Write an expression for the heat given out by steam.

(II) Determine the value of L

50. An electric heater rated 6000W is used to heat 1kg of ice initially at -10^oC until all the mass turns to steam. Given that:

Latent heat of fusion = 334KJkg^-1

Specific heat capacity of ice=2100Jkg^-1k^-1

Specific heat capacity of water=4200Jkg^-1K^-1

Latent heat of vaporization=2260KJkg^-1

(i) Calculate the minimum time required for this activity.

(ii) Explain why the time calculated in (i) above is minimum.

51. (a) Define the following terms:
    • Specific heat capacity of water.
    • Specific latent heat of fusion of ice.

(b) A 200g mass of ice at -14°C was slowly heated by an electric heater of power 30w. The graph below shows how the temperature varies with time.

From the graph above, determine the time corresponding to:

(i) The line QR.

(ii) The line RS

(iii) Hence label the time axis with suitable values and units.

Specific heat capacity of water = 4200J/kgK

Specific latent heat of fusion of ice = 336000J/kgK

(c) Determine a value for the specific heat capacity of ice

(d) Explain why it would be faster to cook food using a Sufuria with an air tight lid than one which is open when at the top   of a high mountain.

52. a) Define specific latent heat of vaporization.
53. Steam at 100^oc was passed for sometime into ice at 0^o At the end, temperature of the water obtained was 52^o_C and its mass 2g.  Calculate;
54. i) The heat lost by steam
55. ii) Mass of the ice used.
56. Other than using steam, describe briefly using a diagram how you would experimentally determine the latent heat of fusion of
57. Give a reason why it is not advisable to melt ice directly using an electric heating coil.
58. a) Define specific latent heat of fusion of a substance.

(b) Figure 10 below shows a block of ice with two heavy weights hanging such that the copper wire connecting them passes over the block.

(i) It is observed that the wire gradually cuts through the ice block, but leaves it as one piece. Explain.

(ii) What change would be observed if the copper wire used in the experiment was placed by a cotton thread?

(c) A block of ice of mass 40g at 0^oC is placed in a calorimeter containing 400g of water at 20^oC. The heat absorbed by the calorimeter is negligible. The final temperature of the mixture after all the ice has melted is T. (specific latent heat of fusion of ice=340,000 J/kg, specific heat capacity of water=4200JKg^-1k^-1)

• Derive an expression for the heat gained by the ice as it melts to water at temperature T.
• (Derive an expression for the heat lost by the water.
• Determine the value of T.

(d) State two differences between boiling and evaporation.

54. (a) Define specific latent heat of vaporization.

(b) In an experiment to determine the specific latent heat of vaporization of a liquid using an electrical method, the amount of heat, Q, required to vaporize a given mass, m, of a liquid were recorded as shown in table 2.

(i) On the grid provided plot a graph of Q (y-axis) against m.

(ii) From the graph, determine the specific latent heat of vaporization of the liquid.

(iii) Suggest a reason why the graph does not pass through the origin.

(iv) Write a possible equation of this graph.

(c) Calculate the amount of heat required to melt 30g of ice at 0^oC. (Latent heat of fusion of ice is 3.34 x 10⁵ Jkg^-1). Give your answer correct to two decimal places.

55. A certain substance contracts when heated at a certain temperature and expands when cooled at the same temperature.

(i)  Name the substance

(ii) State one disadvantage of this behaviour.

(b) The figure 6 below shows four brass pins pressed on a cooking stuck until they are flat on the wood. A white gummed paper was then stuck on the wood covering the pins. The stick was then passed over a Bunsen flame a few times.

It was observed that the paper got charred leaving four white spots. Explain this observation.

(c) The figure 7 below shows an experiment carried out by form one students.

Fig 7

(i)The students dipped two iron rods of the same length but different thickness into a beaker of hot water at the same time. What was the experiment about?

(ii) State and explain the observations made after about 10 minutes.

(iii) If the two rods were much longer, state and explain any difference from C (ii) above that would be made in the observation.

56. (a) What is specific latent heat of fusion?

(b) State two factors which affect freezing point of ice.

(c) Figure 9 below illustrates an experiment in which electrical energy is used to determine specific latent heat of fusion.

Fig 9

• Other than time, state other measurements that would be used to determine the quantity of heat Q, absorbed by ice in unit time.
• Complete the circuit to show connection of the essential circuit components.

(d) In a similar experiment, the following readings were obtained when the heater was switched on for 5 minutes

Voltmeter reading = 6.0V

Ammeter reading = 1.25 A

Temperature rise reading = 10^oC

If by the end of the experiment, 200g of water at 0^oC was collected determine the latent heat of fusion of ice.

57. a) A hot room cannot be cooled by leaving the door of a refrigerator
58. b) The set-up below is used to determine the specific heat capacity of an aluminum block.

Figure 8

1. i) Label the voltmeter and ammeter in the diagram
2. ii) State and explain two precautions taken in the above experiment

iii)    In such an experiment a heater rated 2500w was switched on for 2 minutes. Within this   time the temperature of the block rose from 16º C to 186º C. If the block has a mass of      2kg, what is the specific heat capacity of aluminum?

58. (a) Define the term specific heat capacity

(b)             A student decides to measure the specific heat capacity of aluminium by an electrical method. He selects his apparatus and then assembles the aluminium block, the thermometer and the heating element as shown.

The student intends to substitute his results into the relationship mcT VIt

(i)        Draw a diagram of the electrical circuit he would need to set up in order to be able to carry out the experiment.

(ii)       What other pieces of apparatus would he need?

(iii)      He carries out the experiment and then calculates his value for the specific heat capacity of aluminium. He discovers that his value is higher than the accepted value of 900 J kg-’ K-i. Suggest why his result is higher than 900 J kg^-1 K^-1 .

(iv)      With reference to the apparatus shown in the diagram, state two modifications that he should make in order to minimise the discrepancy.

1……………………

2……………………

(c )     If the specific latent heat of ice is 340000 J kg and the specific latent heat of steam is 2,300,000 J/kg and the specific heat capacity of water is 4200 Jkg – ‘k’ calculate the heat needed to change 2kg of ice at 0°C to steam at 100°C.

59. a) Distinguish between latent heat of fusion and specific latent of fusion.
60. b) Figure 8 shows a block of ice. A thin copper wire with two heavy weights hanging from its ends-passes over the block. The copper wire is observed to pass through the block of ice without cutting it in a process known as regelation.
61. i) Explain this observation,
62. ii) What would be the effect of replacing the copper wire with a cotton thread? Explain.
63. c) Figure 9 shows one method of measuring the specific latent heat of fusion of ice.

Two funnels A and B contain crushed ice at 0°C.

Figure 9

The mass of melted ice from each funnel is measured after 11 minutes. The results are shown below.

Mass of melted ice in A = 24g

Mass of melted ice in B = 63g

(i)        What is the reason for setting up funnel A?

(ii)       Determine the:

1. quantity of heat supplied by the heater.
2. mass of ice melted by the heater.

III.        specific latent heat of fusion of ice.

60. Water of mass 3kg initially at 20°C is heated in an electric kettle rated 3.0kw. The water is heated until it boils at 100°C. Taking specific heat capacity of water to be 4200Jkg’ K’, heat capacity of kettle = 450J/kg, specific latent heat of vaporization of water = 2.3MJ/kg, calculate

(i) The heat absorbed by the water

(ii) Heat absorbed by the electric kettle

(iii) The time taken for the water to boil

(iv) How much longer it will take to boil away all the water

61. (a) State two differences between boiling and evaporation

(b) A metal of mass 10kg is heated to 120⁰C and then dropped into 2kg of water . The final temperature of the mixture is found to be 50⁰ C . Calculate the initial temperature  of the water .(Specify heat capacity of the metal and water is 450Jkg^-1K^-1 and 4200Jkg ^-1 K^-1  respectively )

(c) (i)        Give the property of water which makes it suitable for use as a coolant in machines

(ii) Formation of ice on roads during winter in cold countries is known to hamper vehicles. State two ways in which the melting of ice may be lowered to solve this problem

(d) Figure 11 shows some ether put in a combustion tube and two glass tubes inserted into the tube through a cork. The combustion tube is then put into a small beaker containing some water and a thermometer dipped in the water.

When air is blown into the ether as shown, the reading in the thermometer lowers.             Explain this observation

62. (a) (i) Define the term latent heat of fusion.

(b) In an experiment to determine the power of an electric heater, melting ice was placed  in a container with an outlet and the heater placed in the ice as shown below. The melted ice was collected.

(i) Other than the current and voltage, state the measurement that would be taken to determine the quantity of heat absorbed by the melted ice in unit time.

(ii) If the latent heat of fusion of ice is L, show how measurement in (i) above would be used in determining the power P of the heater.

(iii) It is found that the power determined in this experiment is lower than the manufacturer’s value indicated on the heater. Explain.                                      (

(c) A mass of wax of 1kg was heated uniformly by a 100W heating element until it melted. The graph below shows how the temperature of the wax varies with time.

(i) Explain what is happening in the region.

AB________________________

BC________________________

(ii) Calculate the specific heat capacity of the wax.

(iii) Calculate the specific latent heat of fusion of wax.