Nitrogen dioxide, a pollutant in the atmosphere, can combine with water to form nitric acid. One of the possible reactions is shown here. Calculate ΔG° and K_p for this reaction at 25 °C and comment on the spontaneity of the reaction. 3 NO₂(g) + H₂O(l)→ 2 HNO₃(aq) + NO(g)

Gibbs Free Energy (ΔG°) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic process at constant temperature and pressure. A negative ΔG° indicates that a reaction is spontaneous, while a positive ΔG° suggests non-spontaneity. The value of ΔG° can be calculated using standard enthalpy and entropy changes, providing insight into the favorability of a reaction.

The equilibrium constant (Kp) is a dimensionless value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction, raised to the power of their stoichiometric coefficients. For gaseous reactions, Kp is calculated using partial pressures. The relationship between ΔG° and Kp is given by the equation ΔG° = -RT ln(Kp), linking thermodynamics with chemical equilibrium.

The spontaneity of a reaction refers to its ability to proceed without external intervention. It is determined by the sign of ΔG°; if ΔG° is negative, the reaction is spontaneous under standard conditions. Factors such as temperature, pressure, and concentration can influence spontaneity, and understanding these factors is crucial for predicting the behavior of chemical reactions in various environments.