Understanding the Combined Gas Law

The Combined Gas Law is an amalgamation of Boyle's Law, Charles's Law, and Gay-Lussac's Law. It describes the relationship between the pressure, volume, and temperature of a fixed amount of gas. The law states that the ratio of the product of pressure and volume to the absolute temperature of a gas is constant.

(P1 * V1) / T1 = (P2 * V2) / T2

Where:

• P1 = Initial Pressure
• V1 = Initial Volume
• T1 = Initial Absolute Temperature (in Kelvin)
• P2 = Final Pressure
• V2 = Final Volume
• T2 = Final Absolute Temperature (in Kelvin)

Important: Always use temperature in Kelvin for these calculations! To convert Celsius to Kelvin, add 273.15.

Example Calculation

Let's say a gas initially has a pressure (P1) of 1 atm, a volume (V1) of 10 L, and a temperature (T1) of 273.15 K (0°C). If the pressure changes to 2 atm (P2) and the temperature to 373.15 K (100°C), what is the new volume (V2)?

(1 atm * 10 L) / 273.15 K = (2 atm * V2) / 373.15 K

V2 = (1 atm * 10 L * 373.15 K) / (2 atm * 273.15 K)

V2 ≈ 6.83 L

The new volume of the gas is approximately 6.83 L.