Question

Predict the conditions (high temperature, low temperature, all temperatures, or no temperatures) under which each of the following reactions will be spontaneous. Drag the appropriate items to their respective bins.

a) High temperature
b) Low temperature
c) All temperatures
d) No temperatures

Answer 1

Chemical reactions are spontaneous when Gibbs free energy (ΔG) is negative, which depends on the changes in enthalpy (ΔH) and entropy (ΔS), and the temperature. Reactions with negative ΔH and positive ΔS are spontaneous at all temperatures, while reactions with both ΔH and ΔS negative are spontaneous at low temperatures.

Step-by-step explanation:

The spontaneity of a chemical reaction at constant temperature and pressure is governed by the Gibbs free energy change (ΔG), the reaction will be spontaneous if ΔG is negative and nonspontaneous if ΔG is positive. The sign of ΔG can be determined from the equation ΔG = ΔH - TΔS. Here, ΔH is the change in enthalpy and ΔS is the change in entropy of the system. For a reaction where ΔH is negative and ΔS is positive, the reaction is spontaneous at all temperatures because both terms in the equation contribute to make ΔG negative. For a reaction where ΔH is positive and ΔS is negative, the reaction is nonspontaneous at all temperatures. When ΔH is negative and ΔS is negative, the reaction tends to be spontaneous at low temperatures, because the negative ΔH term dominates. Conversely, when ΔH is positive and ΔS is positive, the reaction tends to be spontaneous at high temperatures because the TΔS term can become larger than ΔH, making ΔG negative.