What would happen to the pressure of a gas if the temperature decreases while the volume is held constant?

Compressing a gas held at a constant temperature

What happens if you take a gas and squeeze it into a smaller volume at a constant temperature? Can we explain what happens in terms of the gas particles?

Think about a piston such as a bicycle pump, with a gas particle bouncing back and forth between the piston head and the opposite wall.

The gas particle causes an outwards pressure on a container walls because it exerts a force on the walls each time it collides and changes direction. With lots of gas particles, the average force of all the collisions acting over the area of the container's walls causes a pressure (p = F/A).

If the temperature is held constant, then the average speed of all the gas particles is also constant. This is because temperature is a measure of the kinetic energy of the gas particles.

If we now push the piston head inwards, squeezing the gas into a smaller volume, then the gas particles now have less space in which to move. The particles collide more frequently with the walls of the container.

This means that the average force exerted by the gas particles on the container walls increases and therefore the gas exerts a greater pressure.

So when the volume of a gas at a constant temperature is decreased (by reducing the container's volume), then the pressure of the gas increases.

GCSE Physics Keywords: Compress, gas, volume, collisions

Course overview

Chemistry Gases Boyle's Law

Boyle's Law is a relationship between pressure and volume at a constant temperature.

#P_1V_1 = P_2V_2#

In this relationship, pressure and volume have an inverse relationship when temperature is held constant.

If there is a decrease in the volume there is less space for molecules to move and therefore they collide more often, increasing the pressure. If there is an increase in the volume the molecules have more space to move, collisions happen less often and the pressure is decreased.

vV ^P ^V vP the relationship is inverse.

However if temperature is involved the relationship between the three values is the combined gas law.

#(PV)/T = (PV)/T#

I hope this was helpful.
SMARTERTEACHER
Boyle's law describes how the pressure of a gas tends to decrease as the volume of a gas increases.

Boyle's Law

When the Volume Decreases, the Pressure increases.

(mass and temperature is constant)