For which of the following reactions does ΔHrxn^∘ represent a heat of formation? a. C(s)+(1)/(2)

step 1 Hello, so in this problem we're just asked to define which of the four equations given, reaction

For which of the following reactions does ΔHrxn^∘ represent...

For which of the following reactions does $\Delta H_{\mathrm{rxn}}^{\circ}$ represent a heat of formation? a. $\mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}(g)$ b. $6 \mathrm{MnO}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Mn}_{3} \mathrm{O}_{4}(s)$ c. $2 \mathrm{Na}(s)+\mathrm{C}(s, \text { graphite })+3 / 2 \mathrm{O}_{2}(g) \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}(s)$ d. $4 \mathrm{H}_{2}(g)+2 \mathrm{C}(s) \rightarrow 2 \mathrm{CH}_{4}(g)$

For which of the following reactions does $\Delta H_{\mathrm{rxn}}^{\circ}$ represent a heat of formation?
a. $\mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}(g)$
b. $6 \mathrm{MnO}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Mn}_{3} \mathrm{O}_{4}(s)$
c. $2 \mathrm{Na}(s)+\mathrm{C}(s, \text { graphite })+3 / 2 \mathrm{O}_{2}(g) \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}(s)$
d. $4 \mathrm{H}_{2}(g)+2 \mathrm{C}(s) \rightarrow 2 \mathrm{CH}_{4}(g)$

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Key Concepts

Elements in Their Standard States

This concept refers to the most stable physical form of an element under standard conditions (usually 1 bar and 25°C). For example, carbon is most stable as graphite, and oxygen as O?(g). Recognizing the standard state is essential for correctly identifying formation reactions, as only elements in their standard state should be involved in the definition of a standard enthalpy of formation.

Standard Enthalpy of Formation

This is the change in enthalpy that accompanies the formation of one mole of a compound from its constituent elements in their most stable (standard) forms under standard conditions. It provides a benchmark for determining the energy associated with forming a compound from basic elements, and is used to calculate reaction enthalpies by Hess’s Law.

Formation Reaction

A formation reaction is a specific type of chemical reaction where one mole of a compound is produced from its elements, each in their standard state. In these reactions, the reactants are the elements in their most stable forms at 1 bar pressure and a standard temperature (typically 25°C), and the reaction enthalpy corresponds to the standard enthalpy of formation of the compound.

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