SUPPLEMENTARY QUESTIONS

THERMAL PROPERTIES OF MATERIALS: Simple Kinetic Model, Specific

Heat Capacities, Specific Latent Heat.

1. Describe the changes to the kinetic energy, the potential energy, and

the total internal energy of the molecules of a block of ice as:

a. it melts at 0 °C, [kinetic energy remains constant, potential energy

increases, internal energy increases]

b. the temperature of the water rises from 0 °C to room

temperature. [kinetic energy increases, no change in potential

energy, internal energy increases]

2. How much heat is absorbed by a 2.8 kg brick sitting in the sun while its

temperature rises from 18 °C to 28 °C? The specific heat capacity of a

brick is 750 J kg-1 K-1. [21000 J]

3. In an experiment to determine a value for the specific heat capacity of

water two students found that the temperature of 0.15 kg of water

rose from 17 °C to 35 °C as the water absorbed 11 kJ of heat energy.

What value did they obtain? [4100 J kg-1 K-1]

4. In the figure below a hypothetical temperature – time curve has been

drawn for 0.60 kg of a solid which is warmed in a well – insulated

container by a 100 W heater.

a. What is the melting point of the solid? [20 °C]

b. Which is greater, the substance’s specific latent heat of fusion or

vaporisation? [specific latent heat of vaporisation]

c. Which is greatest: the substance’s specific heat capacity as a solid,

liquid or gas? [liquid]

d. Determine its specific latent heat of fusion.[20 kJ kg-1]

e. What is its specific heat capacity as a liquid? [1.2 kJ kg-1 K-1]

5. A copper calorimeter has a mass of 50 g and contains 85 g of water at

16 °C. 6.0 g of dried ice is then added and then the contents stirred

until all the ice has melted. What is the temperature of the mixture?

Specific heat capacity of copper = 380 J kg-1 K-1; specific heat capacity

of water = 4190 J kg-1 K-1; specific latent heat of fusion of ice = 334 kJ

kg-1. [10 °C]

6. In an expresso coffee machine steam is bubbled through 200 g of

coffee – flavoured milk taken from a refrigerator at 2 °C. If the final

temperature of the coffee is 90 °C, what mass of steam condensed?

Specific heat capacity of coffee = 4200 J kg-1 K-1; specific latent heat of

vaporisation of water = 2.26 MJ kg-1. [0.032 kg]

7. If 4200 J of heat energy are required to vaporise 5.0 g of ethanol at its

boiling point, what is the specific latent heat of vaporisation of

ethanol? [8.4 × 105 J kg-1]

8. A 2100 W electric kettle containing 1.00 kg of water has just come to

boil. The specific latent heat of vaporisation of water = 2.26 MJ kg-1.

a. How much energy is required to boil all the water away? [2.26 MJ]

b. How long (to the nearest minute) for the kettle to boil dry? [18

min]

9.

a. A 500 W kettle contains 300 g of water at 20 °C. Calculate the

minimum time it would take to raise the temperature of the water

to boiling point. [201 seconds]

b. The kettle is allowed to boil for 2 minutes. Calculate the mass of

the water that remains in the kettle. State any assumptions you

make. [273 g; no energy lost to surroundings, all vapour escapes

from kettle] (Specific heat capacity of water = 4.18 × 103 J kg-1 K-1,

specific latent heat of vaporisation of water = 2.26 × 106 J kg-1)

10.

a. Explain what is meant by the specific heat capacity of a substance.

b. The figure below shows an apparatus used to measure the

specific heat capacity of a copper block of mass 850 g.

The block is initially at 12 °C. The heater is switched on and the

time taken for the temperature to rise to 30 °C is recorded. The

block is cooled to the original temperature, the potential

difference across the heater is increased and the experiment is

repeated.

The results are shown in the table.

i Explain why a thermocouple thermometer is suitable for this

experiment. [small heat capacity, quick acting]

ii Explain why the experiment is repeated using a different

power input.[to allow for energy losses to surroundings]

iii Calculate the specific heat capacity of copper.[372 J kg-1 K-1]