Gas Laws

Charles's Law

Jacques Charles, a French chemist of the early nineteenth century, discovered that, when a gas under constant pressure is heated from 0 degrees Celsius to 1 degree Celsius, it expands 1/273 of its volume. It contracts this amount when the temperature is dropped 1 degree to -1 degree Celsius. Charles reasoned that, if a gas at 0 degrees Celsius was cooled to -273 degree Celsius (actually found to be -273.15 degrees Celsius), its volume would be zero. Actually, all gases are converted into liquids before this temperature is reached. By using the Kelvin scale to rid the problem of negative numbers, we can state Charles's Law as follows:

If the Pressure Remains Constant, the Volume of a Gas Varies Directly as the Absolute Temperature. In other words, volume and temperature are proportionally related.

Boyle's Law

Robert Boyle, a seventeenth century English scientist, found that the volume of a gas decreased when the pressure on it is increased, and vice versa, when the temperature is held constant. Boyle's Law can be stated as follows:

If the Temperature Remains Constant, the Volume of a Gas Varies Inversely as the Pressure Changes.

Pressure versus Temperature

At Constant Volume, the Pressure of a Given Mass of Gas Varies Directly with the Absolute Temperature. In other words, as pressure increases, so does temperature and vice versa.

Dalton's Law of Partial Pressures

When a gas is made up of a mixture of different gases, the total pressure of the mixture is equal to the sum of the partial pressures of the components, that is, the partial pressure of the gas would be the pressure of the individual gas if it alone occupied the volume.

Pressure(total) = P(gas1) + P(gas2) + P(gas3)

Ideal Gas Law

The previous laws discussed do not include the relationship of number of moles of gas to the pressure, volume, and temperature of the gas. A law derived from the kinetic-molecular theory relates these variables. It is called the Ideal Gas Law and is expressed as:

PV = nRT

P, V, T signify Pressure, Volume, and Temperature respectively, but n stands for the number of moles of the gas and R represents the ideal gas constant.

By knowing 4 of the 5 conditions presented in the formula, the fifth one can be found mathematically. The ideal gas constant is always 0.08206 L*atm/mol*K. If this constant is used, remember to convert the Temperature variable to degrees Kelvin.