Chemistry

Chemistry

Problem

Liquid ethanol can be oxidized completely in air according to C2H5OH(l)+3 O2(g)⟶2 CO2(g)+3 H2O(l)\text{C}_2\text{H}_5\text{OH}(l)+3\,\text{O}_2(g)\longrightarrow 2\,\text{CO}_2(g)+3\,\text{H}_2\text{O}(l) The following thermochemical data are provided: 1. 2 C(s, graphite)+3 H2(g)+12 O2(g)⟶C2H5OH(l)ΔH1∘=−277.0 kJ2\,\text{C}(s,\,\text{graphite})+3\,\text{H}_2(g)+\tfrac{1}{2}\,\text{O}_2(g)\longrightarrow \text{C}_2\text{H}_5\text{OH}(l)\qquad \Delta H_1^{\circ}=-277.0\,\text{kJ} 2. C(s, graphite)+O2(g)⟶CO2(g)ΔH2∘=−393.5 kJ\text{C}(s,\,\text{graphite})+\text{O}_2(g)\longrightarrow \text{CO}_2(g)\qquad \Delta H_2^{\circ}=-393.5\,\text{kJ} 3. H2(g)+12 O2(g)⟶H2O(l)ΔH3∘=−285.8 kJ\text{H}_2(g)+\tfrac{1}{2}\,\text{O}_2(g)\longrightarrow \text{H}_2\text{O}(l)\qquad \Delta H_3^{\circ}=-285.8\,\text{kJ} Assume all values refer to 298 K298\,\text{K} and constant pressure. (a) Using Reactions 1–3, calculate the standard molar enthalpy change for the complete oxidation of one mole of liquid ethanol. Express your answer to three significant figures. (b) An engineer claims that doubling each stoichiometric coefficient in the ethanol combustion equation would double the numerical value of the enthalpy change you obtained in part (a). Evaluate the validity of this claim and explain your reasoning.

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