Three reactions are carried out separately in identical, well-insulated calorimeters open to the atmosphere at 298 K. For each reaction, 1.00 mol of the limiting reactant is completely consumed.
Reaction I: 2 NO(g) → N2(g) + O2(g), ΔH° = –180 kJ mol⁻¹ of reaction
Reaction II: NH4NO3(s) → N2O(g) + 2 H2O(l), ΔH° = +25.4 kJ mol⁻¹ of reaction
Reaction III: C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(l), ΔH° = –2.81 MJ mol⁻¹ of reaction
Assume constant pressure conditions and negligible heat capacity of the calorimeter itself.
(a) For each reaction, state whether the surroundings will experience a temperature increase, a temperature decrease, or no temperature change. Justify your answer without performing numerical calculations.
(b) Rank the three reactions in order of the magnitude of the temperature change produced in the surroundings (largest change to smallest change) when 1.00 mol of limiting reactant reacts. Provide reasoning that refers to the given information.
(c) A student claims that Reaction II is the "least energetic" because its enthalpy change has the smallest numerical value. Explain why this statement is incomplete or potentially misleading in the context of the data provided.