Temperature (T)

The temperature of a gas is a measure of the average kinetic energy that the particles have. For a complete discussion of this idea and the difference between temperature and heat, go here.

For most of the unit, we just need to understand that the hotter a gas is, the faster the particles move.

If you want to understand Graham's Law, you will need to know a little more. Specifically, you need to know the formula for kinetic energy.

In this equation, the m stands for the mass and v is the velocity of the particle.

This formula means that the when the velocity doubles, the KE (and therefore the T) quadruples. Or, in a more useful form, if the temperature is quadrupled the molecules are moving twice as fast.

In chemistry, temperature is generally measured in degrees Celsius (occasionally called degrees centigrade), symbolized ^oC. This is the unit that most thermometers found in science classrooms and labs measure. However, we cannot use ^oC in mathematical calculations.

For that reason we also use the kelvin scale, measured in kelvins, K. (Note: the Kelvin scale does NOT use a degree symbol.)

Converting between ^oC and K is done according to the equation:

You can understand the relationship between Celsius and Kelvin by imagining a thermometer that records both temperature scales as seen below.

Absolute zero (on the diagram) will be discussed later in the unit.