The standard enthalpy of combustion of ethene gas [C2 H4(g)] is -1411.1 kJ / mol at 298 K . Give

step 1 So just to start off with some contextual information, we can look at the enthalpy change defini

The standard enthalpy of combustion of ethene gas [C2 H4(g)]...

The standard enthalpy of combustion of ethene gas $\left[\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{g})\right]$ is $-1411.1 \mathrm{kJ} / \mathrm{mol}$ at $298 \mathrm{K} .$ Given the following enthalpies of formation, calculate $\Delta H_{f}^{\circ}$ for $\mathrm{C}_{2} \mathrm{H}_{4}(g)$ $$\begin{array}{ll} \mathrm{CO}_{2}(g) & -393.5 \mathrm{kJ} / \mathrm{mol} \\ \mathrm{H}_{2} \mathrm{O}(l) & -285.8 \mathrm{kJ} / \mathrm{mol} \end{array}$$

Key Concepts

Standard Enthalpy of Combustion

The standard enthalpy of combustion is the amount of heat released when one mole of a substance is completely burned in oxygen under standard conditions. Determining this value helps in understanding the energy content of fuels and allows for the application of Hess' Law to find unknown formation enthalpies.

Reaction Stoichiometry

Reaction stoichiometry involves the quantitative relationships and mole ratios of reactants and products as depicted in a balanced chemical equation. It ensures that all components are correctly accounted for in thermodynamic calculations, such as those using Hess' Law for determining overall reaction enthalpies.

Hess' Law

Hess' Law states that the total enthalpy change of a reaction is independent of the pathway taken, meaning that the enthalpy changes for individual steps in a reaction can be added together to yield the overall reaction enthalpy. This principle is fundamental in calculating unknown enthalpy values by relating them to known standard enthalpies of formation or combustion.

Standard Enthalpy of Formation

The standard enthalpy of formation is the heat change that occurs when one mole of a compound is formed from its elements in their standard states. It serves as a reference point for calculating the enthalpy change of reactions, making it an essential concept in thermochemistry.

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