The standard enthalpy of combustion of methane is Using only this information

CHEMISTRY · Multi-part · A Level · Chemistry · Energetics · Energetics

Problem

The standard enthalpy of combustion of methane is CH4(g)+2 O2(g)→CO2(g)+2 H2O(l)CH_4(g) + 2\,O_2(g) \rightarrow CO_2(g) + 2\,H_2O(l) ΔH∘=−890 kJ\Delta H^\circ = -890\,\text{kJ} Using only this information, consider four related reactions listed below. (1) Part 1: (a) Determine the numerical value of ΔH∘\Delta H^\circ for reactions II, III, and IV. Express each value to the nearest kJ. (2) Part 2: (b) Rank reactions II, I, III, and IV in order of enthalpy change from most exothermic to most endothermic. Clearly indicate ties if any. (3) Part 3: (c) Provide a qualitative justification for the ranking in part (b) based on how scaling a reaction or reversing a reaction affects both the sign and magnitude of ΔH∘\Delta H^\circ.

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