Multiple Choice
When a chemical process is reversed, how do the magnitude and sign of the enthalpy change (ΔH) compare to the original process?
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8. Thermochemistry
First Law of Thermodynamics
Multiple Choice
According to the First Law of Thermodynamics, why are exothermic reactions generally more likely to occur than endothermic reactions?
A
Exothermic reactions release energy to the surroundings, increasing the stability of the system.
B
Exothermic reactions always result in a decrease in entropy.
C
Endothermic reactions increase the temperature of the surroundings.
D
Endothermic reactions require less activation energy than exothermic reactions.
Verified step by step guidance1
Recall the First Law of Thermodynamics, which states that energy cannot be created or destroyed, only transferred or transformed. In chemical reactions, this means the total energy change of the system and surroundings must balance.
Understand that exothermic reactions release energy to the surroundings, usually in the form of heat, which often leads to an increase in the stability of the system because the products have lower energy than the reactants.
Recognize that endothermic reactions absorb energy from the surroundings, which means the system requires an input of energy to proceed, making them generally less spontaneous compared to exothermic reactions.
Consider that the spontaneity of a reaction is influenced not only by enthalpy changes (energy released or absorbed) but also by entropy changes and temperature, as described by the Gibbs free energy equation: \(\Delta G = \Delta H - T\Delta S\).
Conclude that because exothermic reactions release energy and often lead to a decrease in the system's energy, they tend to be more thermodynamically favorable and thus more likely to occur spontaneously than endothermic reactions.
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