The enthalpy changes of the following reactions can be...

The enthalpy changes of the following reactions can be measured: $$\begin{aligned} \mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g}) &+2 \mathrm{H}_{2} \mathrm{O}(\ell) \\ \Delta_{r} H^{\circ} &=-1411.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{r} \mathrm{xn} \\ \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g})+3 \mathrm{H}_{2} \mathrm{O}(\ell) \\ \Delta_{r} H^{\circ}=-1367.5 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} \end{aligned}$$ (a) Use these values and Hess's law to determine the enthalpy change for the reaction $$\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)$$ (b) Draw an energy level diagram that shows the relationship between the energy quantities involved in this problem.

The enthalpy changes of the following reactions can be measured:
$$\begin{aligned}
\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g}) &+2 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\Delta_{r} H^{\circ} &=-1411.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{r} \mathrm{xn} \\
\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CO}_{2}(\mathrm{g})+3 \mathrm{H}_{2} \mathrm{O}(\ell) \\
\Delta_{r} H^{\circ}=-1367.5 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
\end{aligned}$$
(a) Use these values and Hess's law to determine the enthalpy change for the reaction
$$\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\ell)$$
(b) Draw an energy level diagram that shows the relationship between the energy quantities involved in this problem.

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Key Concepts

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is independent of the pathway taken, allowing the use of known enthalpy changes from related reactions to calculate an unknown reaction enthalpy by algebraically combining them.

Reaction Enthalpy

Reaction enthalpy (?H) is the measure of heat absorbed or released during a chemical reaction carried out at constant pressure. It indicates whether a reaction is exothermic (releases heat) or endothermic (absorbs heat) and is crucial for understanding the energy changes involved in chemical processes.

Energy-Level Diagram

An energy-level diagram provides a visual representation of the relative energies of reactants and products. It highlights the overall enthalpy change (?H) of the reaction, clearly indicating the energy difference, which helps in understanding exothermic and endothermic reactions.

State Function

A state function is a property that depends only on the initial and final states of a system and not on the path taken to achieve this state. Enthalpy is an example of a state function, which underpins the application of Hess's Law in determining reaction enthalpies.

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