Chapter 53: Problem 8

Under what conditions can an endothermic reaction occur naturally? Explain your reasoning.

Short Answer

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An endothermic reaction can occur naturally when there is sufficient energy available to be absorbed from the environment and when the reaction is thermodynamically favorable. This generally means that there must be an increase in entropy, or randomness, and the Gibbs free energy (\(\Delta G\)) of the reaction must be negative. A negative \(\Delta G\) can be achieved even if the reaction is endothermic, as long as the increase in entropy (which contributes a negative value when multiplied by the temperature in the \(\Delta G\) equation) is large enough to offset the positive \(\Delta H\).

Step by step solution

Understanding Endothermic Reactions

Endothermic reactions are those in which energy (usually in the form of heat) is absorbed from the environment. These types of reactions often cause the environment to cool down. Examples include photosynthesis and the process of ice melting.

Conditions for Endothermic Reactions

The primary condition for an endothermic reaction to occur is the availability of sufficient energy in the environment that can be absorbed by the reaction. However, simply having energy available is often not enough. The reaction must also be thermodynamically favorable.

Role of Entropy in Endothermic Reactions

Entropy is a measure of disorder or randomness. In many natural endothermic reactions, the entropy of the system increases. This means that the products of the reaction are more disordered or random than the reactants. For example, in the melting of ice, water molecules in the solid state (ice) are arranged in a highly ordered structure. When ice melts (an endothermic reaction), it turns into liquid water, which is far more disordered. The increase in entropy can compensate for the energy absorbed, making the reaction favorable and thus able to occur naturally.

Role of Gibbs Free Energy in Endothermic Reactions

Gibbs Free Energy, represented by the symbol \(\Delta G\), is the energy associated with a chemical reaction that can be used to do work. For a reaction to occur naturally, \(\Delta G\) must be negative. This is defined by the equation \(\Delta G = \Delta H - T\Delta S\), where \(\Delta H\) is the change in enthalpy (energy absorbed or released), T is the absolute temperature, and \(\Delta S\) is the change in entropy. Even if a reaction is endothermic (\(\Delta H > 0\)), it can still occur naturally if the value of \(T\Delta S\) is greater than \(\Delta H\), resulting in a negative \(\Delta G\).

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Under what conditions can an endothermic reaction occur naturally? Explain your reasoning.

Short Answer

Step by step solution

Understanding Endothermic Reactions

Conditions for Endothermic Reactions

Role of Entropy in Endothermic Reactions

Role of Gibbs Free Energy in Endothermic Reactions

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