Which example involves a phase change in which heat energy is released by the substance?
a. freezing ice cream
b. cooking a pot of soup
c. melting ice under sunlight
d. watching frost disappear into air
choose an choice

a). in this case, dh> 0 and sd> 0. if t becomes larger, the term "-tds" will become more negative. at some point, it is possible that -dts will be more negative than the dh is positive, and the reaction will become spontaneous. this is probably the correct answer, but you should look at all of the other possibilities and make sure of that.