Water and Ice
The picture above illustrates the process of water frozen into a solid state, ice. Which of the following statements is correct? (
,
and
mean the change in enthalpy, entropy and Gibbs free energy, respectively.)
a) Both the enthalpy and entropy of the system decrease.
b) If the temperature is lower than
, then (
).
c) If the temperature is higher than
, then
.
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a) Water released energy and formed ice while water molecules become highly ordered; this makes the sentence true;
b) When temperature is lower than 0 ∘ , Δ G < 0 stands for less useful ice; only when the ambient temperature is higher than 0 ∘ , the ice has potential to do work; this makes the statements true;
c) While Δ G > 0 at temperature higher than 0 ∘ to agree as the same as above, with Δ G = Δ H − T Δ S , Δ H > T Δ S does n o t imply ∣ Δ H ∣ > ∣ T Δ S ∣ . This could mean ice absorbs heat for positive Δ H to do work by the system itself, but releases plenty of heat may not allow the system itself to contribute work; ∣ Δ H ∣ > ∣ T Δ S ∣ could turn out to be false always when overall disorder represented by magnitude ought not be smaller than ∣ Δ H ∣ . We can't enjoy having more ice spontaneously while getting an overall output to arrange for less disorder! Quality of energy can only reduce but not increase.
Answer: a ) a n d b )