## Tuesday, September 8, 2020

### Gas Laws and Temperature

General Chemistry Index

Where are we going with this? Getting to the current models of atomic theory didn't happen over night. This page will support the ability to use the kinetic molecular theory with the combined and ideal gas laws to explain changes in volume, pressure, moles and temperature of a gas and apply the ideal gas equation (PV = nRT) to calculate the change in one variable when another variable is changed and the others are held constant.

Gas Laws and Temperature
Yes, there will be math. Eventually.

Temperature is average kinetic energy of the molecules within a substance. An indication of the degree of warmth.

Within the context of the kinetic theory of matter, temperature is the measure of how much energy the molecules have, on average. Another way to think about temperature is (because KE = 1/2mv2) that it tells us how fast the molecules of a substance are moving.

In science, we will use Celsius or Kelvin temperature scales to describe temperature.

To convert:

Celsius = Kelvin - 273.15

Kelvin + 273.15 = Celsius

In dealing with gases, we almost ALWAYS use Kelvin.

How Does Temperature Affect Gases?

When the temperature of a sample of gas in a container goes up…

By definition, this means that the molecules have higher kinetic energy. Therefore:
• if the volume of the container cannot change, the molecules (moving faster) will hit the container more often and with more kinetic energy and raise the pressure.
• if the volume of the container CAN change, the molecules (moving faster) will take up more space (spread out) and increase the volume.
Raising the temperature of a gas will increase its pressure if the volume of the gas and number of molecules are constant.

Opposite: Lowering the temperature of a gas will decrease its pressure if the volume of the gas and number of molecules are constant.

The math… Boyle's Law, Combined Gas Law