Compressed gases provide vital fuels for industry and for homes and farms in rural areas.
Universal Gas Law
Values of the Universal Gas Law Constant, R
||Units for n−
||Units for T−
||Value of R−
Most universal gas law problems are calculated at STP. STP stands for standard temperature and pressure, which is the most commonly calculated temperature and pressure value. STP is defined as 1.00 atm and 0°C, or 273 K.
Determine the volume of 1.00 mol of any gas at STP.
First isolate V from PV=nRT. Then plug in known values and solve.
For any gas at STP, one mole has a volume of 22.4 liters. This can be an extremely convenient conversion factor.
A sample of oxygen gas occupies 10.0 liters at STP. How many moles of oxygen are in the container?
- The universal gas law is PV=nRT, where P is pressure, V is volume, n is number of moles, R is the universal gas law constant, and T is the absolute temperature.
- The value of R varies depending on the units used for P and V. Two common values are 0.0821 L⋅atm/mol⋅K and R=8.314 J/mol⋅K.
- STP is standard temperature and pressure; 273 K and 1.00 atm.
- One mole of a gas at STP has a volume of 22.4 liters.
- The initial pressure in a helium gas cylinder is 30 atm. After many balloons have been blown up, the pressure in the cylinder has decreased to 6 atm while the volume and temperature remain the same. What fraction of the original amount of gas remains in the cylinder?
- Calculate the volume of 8.88 mol of helium gas at 20.0°C and 1.19 atm pressure.
Use this resource to answer the questions that follow.
- Why is it important to have values for R in kPa, atm, and mmHg?
- Why do the units of R include pressure, temperature, volume, and moles?