Gas Calculations

The Ideal Gas Law: The equation of PV = nRT is known as the ideal gas law. Here, P is the pressure exerted by the gas, V is the volume it occupies, n signifies the number of moles in the gas, R is the ideal gas constant and T is the absolute temperature of the gas (in Kelvin).
Units: When using the ideal gas equation, ensure to keep your units consistent. Typically, Pressure (P) is in Pascals (Pa), Volume (V) is in cubic metres (m^3), the number of moles (n) is in moles (mol), and Temperature (T) is in Kelvin (K). The gas constant (R) is often given as 8.315 JK^-1mol^-1.
Calculating Moles: The number of moles in a gas sample can be calculated by rearranging the ideal gas law. If the volume, pressure, and temperature are known, n can be solved for through the equation n=PV/RT.
Molar Volume: Molar volume is the volume occupied by one mole of a substance at a certain pressure and temperature. For any ideal gas at standard temperature and pressure (STP), this value will be approximately 22.4 L.
Partial Pressures: In a mixture of gases, each gas exerts pressure independently of the others. This is known as the gas’ partial pressure, and it can be calculated using Dalton’s law: the total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases.
Gaseous Reactions: In reactions involving gases, use stoicheiometry to determine the amount of reactants and products. Balanced chemical equations show the ratio of moles of one substance to another - these ratios also apply to volumes of gases.
Empirical and Molecular Formulas: The empirical formula of a compound shows the simplest whole-number ratio of atoms of each element in a compound. The molecular formula shows the actual number of atoms of each element in a molecule of the compound. Gas volume ratios can help determine these formulas.
Gases at Different Conditions: If a gas’ pressure, volume, and temperature changes, use the combined gas law to solve for the unknown variable. The combined gas law can be derived from the ideal gas law and is written as P1V1/T1 = P2V2/T2, where P, V, and T are the initial and final pressure, volume, and temperature respectively.
Real Gases: Real gases deviate from ideal behaviour at high pressures and low temperatures. The Van der Waals equation accounts for this non-ideal behaviour by considering the size of gas particles and the attraction between them.
Kinetic Molecular Theory: This theory helps to explain the behaviour of gases. It postulates that a gas consists of a large number of tiny particles moving in random, straight-line motion, and assumes that collisions between particles are perfectly elastic.
Collision Theory and Reaction Rates: Gas reactions occur when molecules collide with sufficient energy and an appropriate orientation. Factors affecting the rate of a gaseous reaction include temperature (increasing temperature increases kinetic energy), pressure (increasing pressure increases the frequency of collisions), and catalysis.