Remember volume V and temperature T are directly proportional to each other at constant pressure P and mass n. If you know that T changes by a factor z, then you can calculate V_{final} = z x V_{initial}

For example, if the temperature of a 3.5 L sample of helium gas is increased from 300 K to 900 K, what is its new volume?

The temperature has increased by a factor of 3 (900/300) so:

V_{final} = z x V_{initial}

V_{final} = 3 x 3.5 L

V_{final} = 10.5 L

**Calculation Tip**

Be sure the temperature is expressed in Kelvin. If you are given a temperature in degrees Celsius or Fahrenheit, convert it to Kelvin before determining the factor z.