Thermal Properties of Matter (Chapter 10)

Internal energy

Internal energy is an energy store that is made up of the total kinetic energy associated with random motion of particles and the total potential energy between particles

Heat capacity definition

Heat capacity C of an object is the change in amount of its internal energy per unit change in its temperature.

Specific heat capacity definition

Specific heat capacity c of a material is the change in amount of its internal energy per unit mass for each unit change in its temperature

How does evaporation lower down temperature

1. Particles in the liquid move at different speeds.

2. Evaporation occurs when the faster particles at the surface of the liquid have enough energy to break away from other liquid particles to escape into the air.

3. After the faster particles have escaped into the air, the particles lefty behind a slightly lower average speed. As temperature decreases with the average kinetic energy of the particles in a body, the liquid slightly cooler than the surroundings. This temperature difference leads to the transfer of energy from the surroundings to the liquid.

Factors affecting the rate of evaporation

• Pressure- when the pressure is higher, the rate of evaporation is lower. At a higher pressure, liquid molecules escape into the air less quickly.

• Humidity of the air- When the humidity is higher, there is a lot of water vapour in the air and the rate of evaporation is lower.

• Surface area of liquid- When the exposed surface area of the liquid is higher, the rate of evaporation is higher. This is because more molecules can escape from the surface of the liquid.

• Temperature- At higher temperature, the average kinetic energy of the liquid molecules is higher. More liquid particle

• Wind speed- wind removes the molecules that have just escaped into the air. Thus, the air surrounding the liquid is drier.

• Boiling point of the liquid- The attractive forces between the particles of the liquid with a lower boiling point is weaker.

Latent Heat

Latent Heat is the energy released or absorbed to change the state of a substance at constant temperature

Latent heat of fusion

Latent heat of fusion is amount of energy transferred to change a substance between solid and liquid states, at constant temperature.

Specific latent heat of fusion

Specific latent heat of fusion is the amount of energy transferred per unit mass of a substance to change between the solid and liquid states, at constant temperature.

Latent heat of vaporisation

Latent heat of vaporisation is the amount of energy transferred to chamber between the liquid and gaseous states, at constant temperature

Specific latent of vaporisation

Specific latent heat of vaporisation is the amount o energy transferred per unit mass of a substance to change between the liquid and gaseous states, at constant temperature