Understanding the Ideal Gas Law
Quick Answer: The Ideal Gas Law (PV = nRT) describes the relationship between pressure, volume, amount, and temperature of an ideal gas. It combines Boyle's, Charles's, and Avogadro's laws into one universal equation.
Key Formula & Variables
PV = nRT where P = pressure, V = volume, n = number of moles, R = universal gas constant, T = absolute temperature in Kelvin. The gas constant R = 0.082057 L·atm/mol·K or 8.314 J/mol·K. Temperature must ALWAYS be in Kelvin (K = °C + 273.15).
Solved Examples
P = 1 atm, V = 22.414 L
T = 273.15 K
n = (1×22.414)/(0.082057×273.15)
n = 1.000 mol
n = 2 mol, V = 10 L
T = 300 K
P = (2×0.082057×300)/10
P = 4.92 atm
n = 0.5 mol, P = 2 atm
T = 400 K
V = (0.5×0.082057×400)/2
V = 8.21 L
FAQs
Gas laws are derived from absolute temperature scales. Using Celsius would lead to negative volumes or pressures at 0°C, which is physically impossible. Zero Kelvin represents absolute zero.
STP (Standard Temperature and Pressure) is defined as 0°C (273.15 K) and 1 atm pressure. At STP, 1 mole of any ideal gas occupies 22.414 L.
It fails at high pressures and low temperatures where intermolecular forces and molecular volume become significant. Real gases deviate and require the van der Waals equation.
R = 0.082057 L·atm/mol·K = 8.314 J/mol·K = 8.314 Pa·m³/mol·K = 1.987 cal/mol·K = 62.36 L·torr/mol·K.