Particle Model of Matter Key Definitions and Model Answers

Internal Energy

The sum of the kinetic and potential energies of all the particles in a system

Specific Latent Heat of Vaporisation

The energy required to change the state of 1 kg of a substance from liquid to gas at a constant temperature.

It is released during condensation and taken in during boiling

Specific Latent Heat of Fusion

The energy required to change the state of 1 kg of a substance from solid to liquid at a constant temperature.

It is released during freezing and taken in when melting

Specific Heat Capacity

The energy required to increase the temperature 1kg of a substance by 1oC

Model Answer: Pressure in a Gas

Gas particles collide with the walls of the container

Pressure in a gas Each collision exerts a force

The force is at right angles to the surface

The pressure is the total force applied over the area of the container in a given time

P=F/A

Model Answer: Pressure in a gas, increasing the temperature

Increasing the temperature increases the speed of gas molecules

There are more frequent collisions with the walls of the container

Each collision exerts a larger force

The total force across the area of the container in a given time increases

So the pressure increases

Model Answer: Pressure in a gas, decreasing the volume TEMPERATURE CONSTANT

There are more frequent collisions with the walls of the container

The total force across the area of the container in a given time increases

So the pressure increases

Boyle's Law

Pressure and volume in a gas are inversely proportional at a constant temperature

Model Answer: Work done on a gas TEMPERATURE CHANGES

Work is done on the gas when decreasing its volume.

This increases the internal energy of a gas

And so the temperature increases.

(the opposite is true if the volume increases)