Glossary
Average Kinetic Energy
Average kinetic energy is the mean energy of motion of the particles in a substance, directly proportional to its absolute temperature.
Example:
When a gas is cooled, its particles slow down, resulting in a decrease in their average kinetic energy.
Avogadro's Law
Avogadro's Law states that equal volumes of all gases, at the same temperature and pressure, have the same number of molecules (or moles).
Example:
If you inflate two balloons to the same size at the same temperature and pressure, one with helium and one with air, Avogadro's Law tells you they contain the same number of gas particles.
Boyle's Law
Boyle's Law states that for a fixed amount of gas at constant temperature, pressure and volume are inversely proportional.
Example:
Squeezing a syringe plunger while blocking the tip demonstrates Boyle's Law as the volume decreases and the pressure inside increases.
Charles' Law
Charles' Law states that for a fixed amount of gas at constant pressure, volume and absolute temperature are directly proportional.
Example:
A balloon left in a cold car shrinks due to Charles' Law, as the lower temperature causes the gas volume to decrease.
Combined Gas Law
The Combined Gas Law relates the pressure, volume, and temperature of a fixed amount of gas, combining Boyle's, Charles', and Gay-Lussac's laws.
Example:
When a weather balloon ascends, its volume changes due to both decreasing atmospheric pressure and decreasing temperature, which can be analyzed using the Combined Gas Law.
Dalton's Law of Partial Pressures
Dalton's Law of Partial Pressures states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases.
Example:
In a scuba tank filled with a mixture of oxygen and nitrogen, the total pressure inside is the sum of the partial pressures of the oxygen and nitrogen, according to Dalton's Law of Partial Pressures.
Gay-Lussac's Law
Gay-Lussac's Law states that for a fixed amount of gas at constant volume, pressure and absolute temperature are directly proportional.
Example:
Heating a sealed aerosol can can be dangerous because, according to Gay-Lussac's Law, the increasing temperature will cause the internal pressure to rise significantly.
Ideal Gas Law
The Ideal Gas Law describes the behavior of an ideal gas using the relationship PV=nRT, where P is pressure, V is volume, n is moles, R is the gas constant, and T is temperature.
Example:
To calculate the number of moles of oxygen gas in a 5.0 L tank at 25°C and 10 atm, you would use the Ideal Gas Law.
Mole Fraction
Mole fraction is a unit of concentration defined as the number of moles of a component divided by the total number of moles in the mixture.
Example:
If a gas mixture contains 2 moles of N2 and 3 moles of O2, the mole fraction of N2 is 2/(2+3) = 0.4.
Partial Pressure
Partial pressure is the pressure that a single gas in a mixture would exert if it alone occupied the same volume at the same temperature.
Example:
If air is 21% oxygen, then the partial pressure of oxygen in the atmosphere at 1 atm total pressure is approximately 0.21 atm.
Pressure
Pressure is a measure of how often gas particles collide with and exert force on the walls of their container.
Example:
When you inflate a balloon, the increasing number of air molecules inside causes more collisions with the balloon's inner surface, leading to higher pressure.
Standard Pressure
Standard Pressure refers to the typical atmospheric pressure at sea level, used as a reference point for gas calculations.
Example:
A gas sample measured at 760 torr is at Standard Pressure, which is equivalent to 1.00 atm.
Standard Temperature
Standard Temperature is a reference temperature of 0 °C (273.15 K) used for comparing gas properties.
Example:
For many gas law problems, you'll need to convert Celsius to Kelvin, especially when dealing with conditions at Standard Temperature.
Standard Temperature and Pressure (STP)
STP is a set of standard conditions for experimental measurements, defined as 0 °C (273.15 K) and 1 atm (760 torr) pressure.
Example:
One mole of any ideal gas occupies 22.4 L at STP.
Temperature
Temperature is a quantitative measure of the average kinetic energy of the particles within a substance.
Example:
Heating a pot of water increases its temperature, causing the water molecules to move faster and have higher kinetic energy.
Universal Gas Constant (R)
The Universal Gas Constant (R) is a proportionality constant that relates the energy scale to the temperature scale in the Ideal Gas Law.
Example:
When using the Ideal Gas Law, ensure your units for pressure, volume, and temperature match the units of the Universal Gas Constant (R), typically 0.08206 L⋅atm/mol⋅K.