Problem 60 - Chemistry: An Atoms-Focused Approach

Question

Are endothermic reactions never spontaneous at low temperature? Explain your answer.

Step-by-Step Solution

Answer

Answer: It is incorrect to say that endothermic reactions are never spontaneous at low temperatures. The spontaneity of a reaction depends on the Gibbs free energy (ΔG), which is determined by the change in enthalpy (ΔH), temperature (T), and change in entropy (ΔS). In some cases, with a sufficiently large positive ΔS value, an endothermic reaction can still occur spontaneously at low temperatures.

Step 1: Understanding Gibbs Free Energy

Gibbs free energy (G) is an essential concept for determining whether a reaction is spontaneous or not. It is represented as: ΔG = ΔH - TΔS Where, ΔG is the change in Gibbs free energy, ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy. If ΔG < 0, the reaction is spontaneous. If ΔG > 0, the reaction is non-spontaneous. If ΔG = 0, the reaction is at equilibrium.

Step 2: Understanding Endothermic Reactions

An endothermic reaction is a chemical reaction that absorbs heat from the surroundings. As a result, the change in enthalpy (ΔH) for an endothermic reaction is positive.

Step 3: Analyzing the Importance of Temperature in Spontaneity

The sign and magnitude of ΔG can highly depend on the temperature. If the temperature is high enough, it can make the reaction spontaneous even if the reaction is endothermic.

Step 4: Analyzing Endothermic Reactions at Low Temperature

For an endothermic reaction with positive ΔH, if the temperature is low, the term TΔS can be smaller than ΔH. This means that the Gibbs free energy ΔG might stay positive, making the reaction non-spontaneous. However, this is not always the case. If the change in entropy (ΔS) is large enough and positive, it can make the reaction spontaneous even at low temperatures, yielding a negative delta G value.

Step 5: Conclusion

It is incorrect to say that endothermic reactions are never spontaneous at low temperatures. The spontaneity of a reaction depends on the Gibbs free energy (ΔG), which is determined by the change in enthalpy (ΔH), temperature (T), and change in entropy (ΔS). In some cases, with a sufficiently large positive ΔS value, an endothermic reaction can still occur spontaneously at low temperatures.