Thermal Properties of Matter

When heat is supplied to a body,

• there is always an increase in the temperature of the body.

• the particles in the body move or vibrate faster.

• there is an increase in the internal energy of the body.

• there is an increase in bonding between the particles.

The increase in temperature when heat is supplied to a body can be explained by

• an increase in the average kinetic energy of the particles in the body.

• an increase in the average spacing of the particles in the body.

• a decrease in the average speeds of the particles in the body.

• a decrease in the internal energy of the particles in the body.

Specific heat capacity is defined as

• the amount of energy required to change a unit mass of a substance from the liquid to the gaseous state.

• the amount of energy required to change a substance from one phase to another.

• the amount of energy required to raise the temperature of a unit mass of a substance by 1°C.

• the amount of energy required to raise the temperature of a substance by 1°C.

A 2.00 kg block of iron has an immersion heater and a thermometer inserted into its body as an experimental set-up for determining the specific heat capacity of iron. The iron block is also well lagged with an insulator.

The heater is set at 100 W. The initial temperature of the iron block is 25°C. After two minutes, its temperature is measured to be 38°C. What is the specific heat capacity of iron?

• 7.7 J kg^–1 °C ^–1

• 160 J kg^–1 °C ^–1

• 240 J kg^–1 °C ^–1

• 462 J kg^–1 °C ^–1

A 300 g block of lead, with a specific heat capacity of 130 J kg^–1 K^–1, is heated to a temperature of 50°C. It is then dropped into a well insulated beaker of water at 30°C. Take the heat capacity of the water and beaker to be 300 J K^–1, and assume that there is no heat loss to the surroundings.

Determine the heat capacity of this block of lead.

• 39 J K^–1

• 130 J K^–1

• 1170 J K^–1

• 1950 J K^–1

A 300 g block of lead, with a specific heat capacity of 130 J kg^–1 K^–1, is heated to a temperature of 50°C. It is then dropped into a well insulated beaker of water at 30°C. Take the heat capacity of the water and beaker to be 300 J K^–1, and assume that there is no heat loss to the surroundings.

When the block of lead is dropped into the water, its temperature decreases, while that of water (and the beaker) increases until they are at the same temperature. Using the Principle of Conservation of Energy, determine the final temperature of the block of lead and the water.

• 32 °C

• 35 °C

• 40 °C

• 42 °C

Why does a pure substance melt at a constant temperature?

• Negligible (i.e. very little) heat is absorbed during this process.

• All pure substances melt at 0°C.

• The heat absorbed during melting is used to increase the kinetic energies of the particles, and not the temperature of the substance.

• The heat absorbed during melting is used to break the bonds between the

  particles.

The specific latent heat of vaporisation of water is 2200 kJ kg^–1, and the specific heat capacity of water is 4200 J kg^–1 K^–1. A heating element is immersed in an insulated cup of water. It takes five minutes to boil the water completely from an initial temperature of 30°C. Assuming no heat is lost to the surroundings, determine the mass of the water if the heating element is operating at 1000 W.

• 0.97 g

• 1.1 g

• 64 g

• 120 g

The specific latent heat of fusion of ice is 3.4 × 10⁵ J kg^–1. Explain what this means.

• The amount of energy needed to melt a piece of ice is 3.4 × 10⁵ J.

• The amount of energy needed to melt a unit mass of ice is 3.4 × 10⁵ J.

• The amount of energy needed to boil a unit mass of water is 3.4 × 10⁵ J.

• The amount of energy needed to boil some water is 3.4 × 10⁵ J.

The rate of evaporation is affected by several factors. Which statement describes one of the factors appropriately?

• Higher air humidity increases the rate of evaporation.

• A smaller exposed area increases the rate of evaporation.

• A lower surrounding temperature increases the rate of evaporation.

• A higher altitude (height above sea level) increases the rate of evaporation.