11.2.2

# Non-Flow Processes

Test yourself

If a gas expands at a constant temperature it is isothermal, if it expands with no heat transfer it is adiabatic.

### Isothermal

• If a gas expands at a constant temperature it is isothermal.
• An isothermal line on a pressure-volume graph is a curved line of constant temperature.
• The product of the pressure and the volume is a constant.
• $pV=constant$

• If a gas expands with no heat transfer it is adiabatic.
• This means the first law becomes:
• ${\Delta}U= W$
• The condition for an adiabatic expansion is:
• $pV^{\gamma}= constant$
• Where $\gamma$ is a constant.

## Constant pressure and volume

Gasses can expand or be compressed under constant pressure or volume.

### Constant pressure

• At constant pressure, the work done by a gas is given by the pressure multiplied by the change in volume. The equation for work done is:
• Work done = pressure x change in volume
• $W=p{\Delta}V$
• Work done is measured in Joules.

### Constant volume

• If a gas is acted on at a constant volume no work is done as ${\Delta}V$ = 0.