Enthalpy change is the measure of energy exchanged between a system and its surroundings during a chemical reaction or physical process. It is represented by the symbol ΔH and can be either positive or negative, indicating an endothermic or exothermic reaction, respectively.
Enthalpy change can be calculated using the formula ΔH = Hproducts - Hreactants, where H represents the enthalpy of the system. The enthalpy values can be obtained from thermodynamic tables or through experimental measurements.
Molar enthalpy change, also known as molar enthalpy of reaction, is the enthalpy change per mole of a substance involved in a reaction. It is calculated by dividing the enthalpy change by the number of moles of the limiting reactant.
To calculate molar enthalpy change, first determine the limiting reactant in the given reaction. Then, divide the enthalpy change by the number of moles of the limiting reactant. The resulting value will be the molar enthalpy change.
Hess's law states that the enthalpy change of a reaction is independent of the pathway taken. This means that the overall enthalpy change can be calculated by adding the enthalpy changes of individual steps, as long as the initial and final states are the same. This can be useful in cases where the enthalpy change of a reaction cannot be directly measured, but can be calculated using known enthalpy values of other reactions.