Write an equation for the formation of each compound from its elements in their standard states, and find ΔH°_rxn for each in Appendix IIB. b. MgCO₃(s)

Key Concepts

Standard States

Standard states refer to the physical states of substances at a defined set of conditions, typically 1 bar of pressure and a specified temperature (usually 25°C). For elements, this means their most stable form at these conditions, such as O2(g) for oxygen and C(s) for carbon. Understanding standard states is crucial for writing formation equations and calculating enthalpy changes.

Formation Reaction

A formation reaction is a chemical reaction that forms one mole of a compound from its constituent elements in their standard states. The equation for such a reaction is essential for determining the enthalpy change (ΔH°) associated with the formation of the compound. For example, the formation of magnesium carbonate (MgCO3) from magnesium, carbon, and oxygen must be represented accurately to calculate its ΔH°.

Enthalpy Change (ΔH°)

Enthalpy change (ΔH°) is the heat content change associated with a chemical reaction at constant pressure. It can be determined using tabulated standard enthalpy values of formation for the reactants and products. For the formation of MgCO3, ΔH° can be calculated by subtracting the total enthalpy of the reactants from that of the products, providing insight into the energy dynamics of the reaction.