The standard enthalpy of formation of NH3(g) is -46.11 kJ /...

The standard enthalpy of formation of $\mathrm{NH}_{3}(\mathrm{g})$ is $-46.11 \mathrm{kJ} / \mathrm{mol} .$ What is $\Delta_{\mathrm{r}} H^{\circ}$ for the following reaction? $$\frac{2}{3} \mathrm{NH}_{3}(\mathrm{g}) \longrightarrow \frac{1}{3} \mathrm{N}_{2}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{g}) \quad \Delta_{\mathrm{r}} H^{\circ}=$$

The standard enthalpy of formation of $\mathrm{NH}_{3}(\mathrm{g})$ is $-46.11 \mathrm{kJ} / \mathrm{mol} .$ What is $\Delta_{\mathrm{r}} H^{\circ}$ for the following reaction?
$$\frac{2}{3} \mathrm{NH}_{3}(\mathrm{g}) \longrightarrow \frac{1}{3} \mathrm{N}_{2}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{g}) \quad \Delta_{\mathrm{r}} H^{\circ}=$$

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Key Concepts

Reaction Enthalpy Calculation

This concept involves determining the overall heat change in a chemical reaction by using the formula ?H° = ??H_f°(products) - ??H_f°(reactants). It leverages known standard enthalpy values and the stoichiometric coefficients from the balanced reaction to compute the net enthalpy change.

Stoichiometry in Thermochemistry

In thermochemistry, stoichiometry relates the coefficients in a balanced chemical equation to the quantities of substances involved. Correctly using these coefficients ensures that the enthalpy changes are accurately scaled according to the actual amounts of reactants and products in the reaction.

Standard Enthalpy of Formation

This is the energy change when one mole of a compound is formed from its elements in their standard states. It serves as a reference value for calculating the enthalpy changes of reactions, allowing one to determine the energy absorbed or released during compound formation.

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is independent of the pathway taken. This principle allows the calculation of reaction enthalpies by summing the standard enthalpies of formation for the products and subtracting those for the reactants.

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