The Ideal Gas Law

Gas particles are constantly zooming around and bouncing off the walls of their container, and that is what creates pressure. Squeeze the gas into a smaller volume, heat it up, or add more gas particles, and the pressure rises, because the molecules crowd together or move faster and hit the walls harder and more often. The ideal gas law ties pressure, volume, amount of gas, and temperature together in one equation.

P · V = n · R · T

• P — pressure (Pa): the force per unit area the gas exerts on the walls of its container
• V — volume (m³): the amount of space the gas occupies
• n — amount of substance (mol): how many moles of gas particles are present
• R — gas constant (J/(mol·K)): a fixed number that connects the units of pressure, volume, amount, and temperature
• T — temperature (K): how hot the gas is, measured on the kelvin scale

A container holds 1 mole of gas at a temperature of 300 kelvin, squeezed into a volume of 3 cubic meters. What pressure does the gas exert?

• n = 1 mol
• T = 300 K
• V = 3 m³

1. P = n · R · T / V
2. P = (1 mol · 8.31 J/(mol·K) · 300 K) / 3 m³

P = 831 Pa

If the temperature drops to 200 kelvin while the volume and amount of gas stay the same, what is the new pressure?

• 554 Pa
• 831 Pa
• 1662 Pa

A balloon at constant pressure and amount of gas doubles in volume. What must happen to its temperature?

• It stays the same
• It doubles
• It is cut in half