The following reaction is spontaneous at all temperatures: CaC₂(s)+ 2H₂O(l)→ Ca(OH)₂(s)+ C₂H₂(g) Which of the following statements is true? A)ΔH is negative and ΔS is positive. B)ΔH is negative and ΔS is negative. C)ΔH is positive and ΔS is negative. D)ΔH is positive and ΔS is positive. E)ΔG is positive at all temperatures.

Question

Quizplus · Accepted Answer

The fact that the reaction is spontaneous at all temperatures means that ΔG is negative at all temperatures. The equation relating ΔG to ΔH and ΔS is ΔG = ΔH - TΔS, where T is the temperature in Kelvin. For ΔG to be negative at all temperatures, either ΔH must be negative, or TΔS must be positive. Since the reaction involves a solid and a liquid that are forming a solid and a gas, we can assume that ΔS is positive (there is an increase in entropy). Therefore, ΔH must be negative to make the entire term negative and thus favor a negative ΔG.

The Following Reaction Is Spontaneous at All Temperatures