The complete combustion of methane, CH41g2, to form H2O1l2 and CO21g2 at constant pressure releases 890 kJ of heat per mole of CH4. (b) Draw an enthalpy diagram for the reaction.

Key Concepts

Enthalpy (H)

Enthalpy is a thermodynamic property that represents the total heat content of a system at constant pressure. It is defined as the sum of the internal energy and the product of pressure and volume (H = U + PV). In chemical reactions, changes in enthalpy (ΔH) indicate whether a reaction is exothermic (releases heat) or endothermic (absorbs heat), which is crucial for understanding energy changes during combustion.

Combustion Reaction

A combustion reaction is a chemical process in which a substance (typically a hydrocarbon) reacts with oxygen to produce carbon dioxide and water, releasing energy in the form of heat. In the case of methane (CH4), its complete combustion yields CO2 and H2O, and is characterized by a significant release of energy, as indicated by the 890 kJ of heat released per mole of CH4 in the question.

Enthalpy Diagram

An enthalpy diagram visually represents the changes in enthalpy during a chemical reaction. It typically shows the enthalpy of the reactants and products, along with the enthalpy change (ΔH) for the reaction. For the combustion of methane, the diagram would illustrate the higher enthalpy of the reactants compared to the lower enthalpy of the products, indicating the exothermic nature of the reaction and the energy released.