Topic 3 Thermal Energy RGA

The fraction of the internal energy that is due to molecular vibration varies in the different states of matter. What gives the order from highest fraction to lowest fraction of internal energy due to molecular vibration?

• liquid > gas > solid

• solid > liquid > gas

• solid > gas > liquid

• gas > liquid > solid

A mass m of ice at a temperature of –5 °C is changed into water at a temperature of 50 °C.

Specific heat capacity of ice = c_i

Specific heat capacity of water = c_w

Specific latent heat of fusion of ice = L

Which expression gives the energy needed for this change to occur?

• 55 m c_w + m L

• 55 m c_i + 5 m L

• 5 m c_i + 50 m c_w + m L

• 5 m c_i + 50 m c_w + 5 m L

A liquid is initially at its freezing point. Energy is removed at a uniform rate from the liquid until it freezes completely.

Which graph shows how the temperature T of the liquid varies with the energy Q removed from the liquid?

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Energy is supplied at a constant rate to a fixed mass of a material. The material begins as a solid. The graph shows the variation of the temperature of the material with time.

The specific heat capacities of the solid, liquid and gaseous forms of the material are c_s c_l and c_g respectively. What can be deduced about the values of c_s c_l and c_g?

• c_s > c_g > c_l

• c_l > c_s > c_g

• c_l > c_g > c_s

• c_g > c_s > c_l

Which of the following is numerically equal to the specific heat capacity of the substance of a solid body?

• The thermal energy required to melt the body

• The thermal energy required to increase the temperature of unit mass of the body by 1K

• The thermal energy required to increase the temperature of the body by 1K

• The total kinetic and potential energy of all the molecules in the body

Which of the following is equivalent to a temperature of –100°C?

• –373 K

• –173 K

• 173 K

• 373 K

A fixed mass of water is heated by an electric heater of unknown power P. The following quantities are measured

I. mass of water

II. increase in water temperature

III. time for which water is heated.

In order to calculate P, the specific heat capacity of the water is required. Which are also required?

• I and II only

• I and III only

• II and III only

• I, II and III

A pure solid is heated at its melting point. While it is melting the

• mean kinetic energy of the molecules of the solid increases.

• mean potential energy of the molecules of the solid increases.

• temperature of the solid increases.

• temperature of the solid decreases.

The energy of the molecules of an ideal gas is

• thermal only.

• thermal and potential.

• potential and kinetic.

• kinetic only.

Find the energy released by a copper block when it is cooled from 100^°C to 20^°C. Given that the heat capacity of the block is 770 J^°C^-1.

• 7.70x10⁴ J

• 8.61x10⁴ J

• 6.16x10⁴ J

• 5.02x10⁴ J