Why does temperature increase if you increase pressure with an ideal gas?

Question

I know that pressure increases if you increase temperature and why, but why does it occur the other way around? Thanks!

Answer 1

Everyone unnescessarily appeals to statistical models of molecules and miss the point - you can quite happily have very high pressure at very low temperature when molecules are moving very slowly.

Why temperature rises is very easy to understand classically.

Temperature is a measure of energy in the system. To increase the pressure of a fixed mass of gas you have to compress it. This means applying a force against the pressure of the gas and moving it through a distance. A force moved through a distance means expending energy. This energy goes into the gas. The gas now has more energy, so its temperature rises.

QED.

Answer 2

The work done on a gas with pressure P due to a change in volume dV is -PdV. That work goes into increasing the kinetic energy of the gas molecules, which means increasing the temperature. That's the fluid description. From a molecular point of view, an elastic collision off an inwardly moving wall will result in result in an increase in the molecule's speed, just as a baseball increases it's speed when it collides with a moving bat.

Answer 3

Well, to start...the Ideal Gas Law is one of the largest and most complex of the gas laws. This is in part because of the number of variables in the equation...and in part due to the abstraction of an 'ideal gas' that the law is built on--it was designed as a sort of umbrella for Boyle's, Charles', and Avogadro's laws.

As for why it does not occur the other way around...ideal gases have molecular volume and show no attraction between molecules at any distance; real gas molecules have volume and show attraction at short distances. Thus, pressure at high degrees will bring the molecules very close together. This causes more collisions and also allows the weak attractive forces to come into play. With low temperatures, the molecules do not have enough energy to continue on their path to avoid that attraction...

Answer 4

Temperature in a gas is simply a statistical measure of the average energy or velocity of the individual particles. When the pressure on the gas is increased (volume decreased) the particles move with a higher velocity in a more confined space, thus the temperature rises.

Answer 5

The equation is PV = nRT. But you probably know that. Explaining why is a bit trickier.

Short of referring you to the statistical mechanical derivation on the wiki page, the best I could do would be to say that if pressure goes up, then the gas particles must be hitting the wall harder or more often. If density doesn't change, that means the gas particles must be going faster, which means the temperature must be higher.

Answer 6

This is Gay Lussac's Law that states that: -
"The Absolute Temperature (K) of a gas is Directly Proportional to its Absolute Pressure at Constant Volume".

P1/P2 = T1/T2...Cross multiply to give:- P1 x T2 = P2 x T1.

Temperature Increase <====>Pressure Increase
**Pressure Decrease <====> Temperature Decrease.
**(Also one of the principles of Refrigeration).

With increase in temperature, the molecules have more Kinetic Energy and are colliding more with their container sides and each other resulting in an increase in pressure.
(and vice-versa).

Answer 7

The product of volume and pressure should be a constant in an ideal gas. Boyle's Law.

Answer 8

The more pressure the faster the molecules bounce off each other and the walls... and the faster they move the higher the temperature gets. ex. Ice molecules are tightly packed slow moving, water a little faster, gas(vapor) move much quicker and hotter. I like to think of a ballon to help me understand the concept.

Answer 9

Temperature is just a measure of molecular movement.

You take a bunch of molecules flying around in a gas and shove them into a smaller space, and they're going to be colliding and accelerating in various directions more often.

Think about putting 10 kids in a field, then in a day care center, then stuffing them in a closet. It's like that.

Answer 10

Temp is simply the motion of the atoms.

If you increase pressure, the atoms are more crowded and collide much more, creating heat.