Gas Law Calculator (Combined)
Calculate an unknown variable using the Combined Gas Law: (P1 * V1) / T1 = (P2 * V2) / T2. Remember to use Kelvin for temperature!
Result
---
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.
Quick FAQs
- Why must I use Kelvin?
- Gas laws are based on absolute zero. Using Celsius or Fahrenheit (which can be 0 or negative) would lead to mathematical errors like division by zero or negative volumes.
- What units should I use for Pressure and Volume?
- You can use any units (atm, kPa, mmHg for pressure; L, mL, m³ for volume) as long as you are consistent for both initial (1) and final (2) states.
- What is Standard Temperature and Pressure (STP)?
- Commonly, STP is defined as 0°C (273.15 K) and 1 atm of pressure.