Multiple Choice
Given the reaction: 2H_2(g) + O_2(g) ightarrow 2H_2O(l), predict whether this reaction is exothermic or endothermic.
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8. Thermochemistry
Endothermic & Exothermic Reactions
Multiple Choice
In thermochemistry, what is known about a reaction with a positive enthalpy change ?
A
The reaction must be spontaneous at all temperatures ().
B
The reaction is endothermic and absorbs heat from the surroundings.
C
The reaction has no heat exchange with the surroundings ().
D
The reaction is exothermic and releases heat to the surroundings.
Verified step by step guidance1
Understand that the enthalpy change, denoted as \(\Delta\Delta H\), represents the heat absorbed or released by a system during a reaction at constant pressure.
Recognize that a positive enthalpy change (\(\Delta\Delta H > 0\)) means the system absorbs heat from the surroundings, indicating the reaction is endothermic.
Recall that an endothermic reaction requires energy input, so heat flows into the system, increasing its enthalpy.
Note that this does not necessarily mean the reaction is spontaneous; spontaneity depends on the Gibbs free energy change (\(\Delta\Delta G\)), which involves both enthalpy and entropy changes.
Conclude that the correct interpretation of a positive \(\Delta\Delta H\) is that the reaction is endothermic and absorbs heat from the surroundings.
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