Using the thermochemical equations in Exercise 5.67 as...

Using the thermochemical equations in Exercise 5.67 as needed and in addition $$ \begin{aligned} \mathrm{CH}_{4}(\mathrm{~g})+2 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{CO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\ell) & \\ \Delta H=-890 \mathrm{~kJ} \end{aligned} $$ calculate $\Delta H$ for $$ \mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{~g})+2 \mathrm{H}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{CH}_{4}(\mathrm{~g}) \quad \Delta H=? $$

Using the thermochemical equations in Exercise 5.67 as needed and in addition
$$
\begin{aligned}
\mathrm{CH}_{4}(\mathrm{~g})+2 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{CO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\ell) & \\
\Delta H=-890 \mathrm{~kJ}
\end{aligned}
$$
calculate $\Delta H$ for
$$
\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{~g})+2 \mathrm{H}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{CH}_{4}(\mathrm{~g}) \quad \Delta H=?
$$

Key Concepts

Reaction Stoichiometry

Reaction stoichiometry involves using the quantitative relationships between reactants and products in a chemical equation. It is crucial for ensuring that the conservation of mass is maintained and for accurately relating the amounts of substances involved in energy calculations, such as those using Hess's Law.

Enthalpy Change (?H)

Enthalpy change, denoted as ?H, is the heat change at constant pressure during a chemical reaction. It quantifies the energy transferred as heat between the system and its surroundings. Understanding ?H is fundamental when analyzing reaction energetics, such as determining the feasibility of chemical processes.

Hess's Law

Hess's Law is a principle in thermochemistry stating that if a reaction can be expressed as the sum of several steps, then the enthalpy change of the overall reaction is the sum of the enthalpy changes for each step. This law allows for the determination of enthalpy changes that cannot be measured directly by combining known enthalpy changes from other reactions.

Thermochemical Equations

Thermochemical equations are chemical equations that include the enthalpy change (?H) for the reaction, indicating whether the reaction is exothermic or endothermic. They provide insight into how energy is absorbed or released during chemical reactions, and are essential for calculations involving reaction energetics.

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