Multiple Choice
A solid salt dissolves in water according to the following thermochemical equation: NaCl(s) → Na^+(aq) + Cl^-(aq); ΔH = +3.9 kJ/mol. Which statement correctly describes the enthalpy of solution for NaCl(s)?
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8. Thermochemistry
Thermochemical Equations
Multiple Choice
In a thermochemical equation carried out at constant pressure, what does the enthalpy of reaction, , measure?
A
The activation energy required for the reaction to occur
B
The change in temperature of the surroundings for any amount of reactants
C
The heat absorbed or released by the reaction at constant pressure
D
The total kinetic energy of the reactant molecules
Verified step by step guidance1
Understand that enthalpy of reaction, denoted as \(\Delta\mathrm{H}_{\mathrm{rxn}}\), is a thermodynamic quantity measured under constant pressure conditions.
Recall that \(\Delta\mathrm{H}_{\mathrm{rxn}}\) represents the heat exchanged between the system (the reacting substances) and the surroundings during the reaction.
Recognize that this heat exchange can be either absorbed (endothermic reaction) or released (exothermic reaction) by the reaction mixture.
Note that \(\Delta\mathrm{H}_{\mathrm{rxn}}\) does not measure activation energy, temperature change of surroundings, or total kinetic energy of molecules; it specifically quantifies heat flow at constant pressure.
Therefore, \(\Delta\mathrm{H}_{\mathrm{rxn}}\) measures the heat absorbed or released by the reaction at constant pressure.
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