Use standard enthalpies of formation to calculate ΔH°_rxn for each reaction. d. Cr₂O₃(s) + 3 CO(g) → 2 Cr(s) + 3 CO₂(g)

Verified step by step guidance

1. Identify the standard enthalpies of formation (ΔH°f) for each reactant and product in the reaction. These values are typically found in a table in your textbook or a reliable chemistry database. For this reaction, you need the ΔH°f for Cr2O3(s), CO(g), Cr(s), and CO2(g).
2. Write the balanced chemical equation and note the stoichiometric coefficients. For this reaction, it is already balanced as: Cr2O3(s) + 3 CO(g) → 2 Cr(s) + 3 CO2(g).
3. Apply the formula for calculating the standard enthalpy change of the reaction (ΔH°rxn): ΔH°rxn = ΣΔH°f (products) - ΣΔH°f (reactants). Remember to multiply the ΔH°f of each substance by its stoichiometric coefficient in the balanced equation.
4. Substitute the ΔH°f values into the equation. Multiply each ΔH°f by the respective coefficients from the balanced equation: ΔH°rxn = [2(ΔH°f for Cr) + 3(ΔH°f for CO2)] - [ΔH°f for Cr2O3 + 3(ΔH°f for CO)].
5. Simplify the expression to find the ΔH°rxn. This will give you the standard enthalpy change for the reaction, which indicates whether the reaction is exothermic or endothermic.

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 value, 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 that 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 Stoichiometry

Reaction stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. It is essential for balancing chemical equations and determining the amounts of substances consumed and produced. In the context of calculating ΔH°rxn, stoichiometry helps in applying the correct coefficients from the balanced equation to the standard enthalpy values to ensure accurate calculations.