(a) What is meant by the term standard conditions with reference to enthalpy changes? (b) What is meant by the term enthalpy of formation? (c) What is meant by the term standard enthalpy of formation?

(a) The term standard conditions with reference to enthalpy changes refers to specific reference conditions used to report and compare the values of thermodynamic properties like enthalpy changes. These conditions typically include a pressure of 100 kPa (1 bar), a temperature of \(298.15\ K\) (25°C), and sometimes mention the concentration of the reactants and products as 1 M and partial pressures of gaseous substances as 1 atm. (b) Enthalpy of formation, or heat of formation, refers to the change in enthalpy during the formation of 1 mole of a substance from its constituent elements in their most stable forms. It is the energy change associated with the production of a compound from its basic elements and can be calculated as \(ΔH_f = H_{products} - H_{reactants}\). (c) The standard enthalpy of formation, denoted as \(ΔH^⦵_f\), refers to the enthalpy change occurring when one mole of a substance is formed from its elemental components under standard conditions. It allows for the calculation of overall enthalpy changes for any chemical reaction using the known standard enthalpies of formation for each reactant and product involved in the reaction, according to Hess's law.