Use standard enthalpies of formation to calculate ΔH°_rxn for each reaction. d. N₂O₄(g) + 4 H₂(g) → N₂(g) + 4 H₂O(g)

Verified step by step guidance

1. Identify the standard enthalpy of formation (ΔH°f) for each reactant and product in the reaction. These values are typically found in tables in chemistry textbooks or reliable online resources.
2. Write the balanced chemical equation: N₂O₄(g) + 4 H₂(g) → N₂(g) + 4 H₂O(g).
3. Apply the formula for the standard enthalpy change of the reaction: ΔH°rxn = Σ(ΔH°f of products) - Σ(ΔH°f of reactants).
4. Calculate the sum of the standard enthalpies of formation for the products: [ΔH°f(N₂(g)) + 4 * ΔH°f(H₂O(g))].
5. Calculate the sum of the standard enthalpies of formation for the reactants: [ΔH°f(N₂O₄(g)) + 4 * ΔH°f(H₂(g))]. Subtract the sum of the reactants from the sum of the products to find ΔH°rxn.

Key Concepts

Enthalpy of Formation

The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It is a crucial value used in thermodynamics to calculate the heat changes in chemical reactions. Each substance has a specific ΔH°f, which can be found in tables, and is essential for determining the overall enthalpy change of a reaction.

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the number of steps taken to achieve the reaction. This principle allows chemists to calculate the enthalpy change of a reaction by summing the enthalpy changes of individual steps, making it possible to use standard enthalpies of formation to find ΔH°rxn for complex reactions.

Reaction Enthalpy Change (ΔH°rxn)

The reaction enthalpy change (ΔH°rxn) is the difference between the total enthalpy of the products and the total enthalpy of the reactants. It indicates whether a reaction is exothermic (releases heat, ΔH°rxn < 0) or endothermic (absorbs heat, ΔH°rxn > 0). Calculating ΔH°rxn using standard enthalpies of formation involves subtracting the sum of the ΔH°f values of the reactants from that of the products.