Methanol (CH₃OH) burns in oxygen to form carbon dioxide and water. Write a balanced equation for the combustion of liquid methanol and calculate ΔH°_rxn, ΔS°_rxn, and ΔG°_rxnat 25 °C. Is the combustion of methanol spontaneous?

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Write the unbalanced chemical equation for the combustion of methanol: \( \text{CH}_3\text{OH} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \).

Balance the chemical equation by ensuring the number of atoms of each element is the same on both sides: \( 2\text{CH}_3\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 4\text{H}_2\text{O} \).

Use standard enthalpies of formation to calculate \( \Delta H^\circ_{\text{rxn}} \) using the formula: \( \Delta H^\circ_{\text{rxn}} = \sum \Delta H^\circ_{\text{f,products}} - \sum \Delta H^\circ_{\text{f,reactants}} \).

Calculate \( \Delta S^\circ_{\text{rxn}} \) using standard molar entropies: \( \Delta S^\circ_{\text{rxn}} = \sum S^\circ_{\text{products}} - \sum S^\circ_{\text{reactants}} \).

Determine \( \Delta G^\circ_{\text{rxn}} \) using the Gibbs free energy equation: \( \Delta G^\circ_{\text{rxn}} = \Delta H^\circ_{\text{rxn}} - T\Delta S^\circ_{\text{rxn}} \), and assess spontaneity by checking if \( \Delta G^\circ_{\text{rxn}} < 0 \).

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Combustion Reactions

Combustion reactions are exothermic processes where a substance reacts with oxygen to produce heat, light, carbon dioxide, and water. In the case of methanol (CH3OH), the balanced equation for its combustion involves the complete reaction with oxygen to yield carbon dioxide (CO2) and water (H2O). Understanding how to balance these equations is crucial for stoichiometric calculations and thermodynamic assessments.

Thermodynamics: ΔH°, ΔS°, and ΔG°

Thermodynamics involves the study of energy changes in chemical reactions. ΔH° (enthalpy change) indicates the heat absorbed or released, ΔS° (entropy change) measures the disorder or randomness in the system, and ΔG° (Gibbs free energy change) determines the spontaneity of the reaction. A negative ΔG° suggests that the reaction is spontaneous under standard conditions, which is essential for evaluating the combustion of methanol.

Spontaneity of Reactions

The spontaneity of a reaction refers to its ability to occur without external intervention. It is determined by the sign of ΔG°; if ΔG° is negative, the reaction is spontaneous. Factors influencing spontaneity include enthalpy and entropy changes, where a highly exothermic reaction with a significant increase in entropy is likely to be spontaneous, as is the case with the combustion of methanol.

Methanol (CH3OH) burns in oxygen to form carbon dioxide and water. Write a balanced equation for the combustion of liquid methanol and calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C. Is the combustion of methanol spontaneous?