Answer to Question #316489 in General Chemistry for John

Question

Discuss standard state and give examples (Padolina et al., 1995)

Answer 1

The standard state of a material is a reference point for the material’s thermodynamic state properties such as enthalpy, entropy, Gibbs free energy, etc. It is used to calculate the material’s properties under different conditions and is denoted as

H

⊖

f

.

The standard state for a gas is the hypothetical state at 1 bar; for liquids and solids, the pure substance at 1 bar; for elements, the most stable allotrope of the element; and for a substance in solution (solute), concentration at 1 M and 1 bar.

The standard enthalpy of formation is the change in enthalpy that accompanies the formation of one mole of the compound from its elements. The standard enthalpy of reaction occurs in a system when one mole of matter is transformed by a chemical reaction.