Consider this reaction occurring at 298 K: N₂O(g) + NO₂(g) ⇌ 3 NO(g) a. Show that the reaction is not spontaneous under standard conditions by calculating ΔG°_rxn.

검증된 단계별 안내

insert step 1> Calculate the standard Gibbs free energy of formation (ΔG°f) for each species involved in the reaction using a standard table of thermodynamic values.

insert step 2> Use the equation ΔG°rxn = ΣΔG°f(products) - ΣΔG°f(reactants) to find the standard Gibbs free energy change for the reaction.

insert step 3> Substitute the ΔG°f values for NO, N2O, and NO2 into the equation. Remember to multiply the ΔG°f of NO by 3, as there are 3 moles of NO produced.

insert step 4> Calculate the sum of the ΔG°f values for the products and the reactants separately.

insert step 5> Subtract the sum of the reactants' ΔG°f from the sum of the products' ΔG°f to find ΔG°rxn. If ΔG°rxn is positive, the reaction is not spontaneous under standard conditions.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Gibbs Free Energy (ΔG)

Gibbs Free Energy (ΔG) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. A negative ΔG indicates that a reaction is spontaneous, while a positive ΔG suggests non-spontaneity. The standard Gibbs free energy change (ΔG°) is calculated using standard state conditions, which allows for the comparison of different reactions.

Standard Conditions

Standard conditions refer to a set of specific conditions used to measure and compare the properties of substances, typically defined as 1 bar of pressure and a specified temperature, usually 298 K (25 °C). Under these conditions, the standard enthalpy, entropy, and Gibbs free energy values are determined, providing a consistent basis for evaluating the spontaneity of reactions and their thermodynamic favorability.

Equilibrium Constant (K)

The equilibrium constant (K) is a dimensionless value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. It is related to the Gibbs free energy change by the equation ΔG° = -RT ln(K), where R is the universal gas constant and T is the temperature in Kelvin. A K value less than 1 indicates that reactants are favored at equilibrium, which correlates with a positive ΔG°, suggesting the reaction is not spontaneous under standard conditions.

Consider this reaction occurring at 298 K: N2O(g) + NO2(g) ⇌ 3 NO(g) a. Show that the reaction is not spontaneous under standard conditions by calculating ΔG°rxn.