Given the following thermochemical equations, 3 Mg(s)+2 NH3(g) ⟶Mg3 N2(s)+3 H2(g) ΔH^∘=-371 kJ

step 1 Okay, let's try to use Hess's law to take the two equations on the top and somehow get them to b

Given the following thermochemical equations, 3 Mg(s)+2...

Given the following thermochemical equations, $$ 3 \mathrm{Mg}(s)+2 \mathrm{NH}_{3}(g) \longrightarrow \mathrm{Mg}_{3} \mathrm{~N}_{2}(s)+3 \mathrm{H}_{2}(g) $$ $\Delta H^{\circ}=-371 \mathrm{~kJ}$ $$ \frac{1}{2} \mathrm{~N}_{2}(g)+\frac{3}{2} \mathrm{H}_{2}(g) \longrightarrow \mathrm{NH}_{3}(g) \quad \Delta H^{\circ}=-46 \mathrm{~kJ} $$ calculate $\Delta H^{\circ}$ (in kilojoules) for the following reaction: $$ 3 \mathrm{Mg}(s)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{Mg}_{3} \mathrm{~N}_{2}(s) $$

Given the following thermochemical equations,
$$
3 \mathrm{Mg}(s)+2 \mathrm{NH}_{3}(g) \longrightarrow \mathrm{Mg}_{3} \mathrm{~N}_{2}(s)+3 \mathrm{H}_{2}(g)
$$
$\Delta H^{\circ}=-371 \mathrm{~kJ}$
$$
\frac{1}{2} \mathrm{~N}_{2}(g)+\frac{3}{2} \mathrm{H}_{2}(g) \longrightarrow \mathrm{NH}_{3}(g) \quad \Delta H^{\circ}=-46 \mathrm{~kJ}
$$
calculate $\Delta H^{\circ}$ (in kilojoules) for the following reaction:
$$
3 \mathrm{Mg}(s)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{Mg}_{3} \mathrm{~N}_{2}(s)
$$

Key Concepts

Reaction Scaling and Manipulation

When using given thermochemical equations to calculate the enthalpy change for a related reaction, the equations may need to be scaled (multiplied by appropriate factors) or reversed so that the reactants and products match the desired overall reaction. Scaling directly multiplies the enthalpy change by the same factor as the stoichiometric coefficients, while reversing the reaction changes the sign of the enthalpy change.

Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. In the context of calculating enthalpy changes, stoichiometric coefficients indicate how many moles of each substance partake in the reaction, which is crucial for correctly scaling the enthalpy changes in thermochemical equations.

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps into which the reaction can be divided. This principle is based on the fact that enthalpy is a state function, meaning its change depends only on the initial and final states of the system, not on the pathway between them.

Thermochemical Equations

Thermochemical equations are chemical equations that include not only the reactants and products but also the enthalpy change associated with the reaction. They provide a complete description of the energy changes occurring during a chemical process, which allows for the calculation of energy changes for related reactions when combined appropriately.

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