in which energy is consumed—can proceed spontaneously if it’s
accompanied by a large enough increase in entropy.
- C You should associate enthalpy with the words “exothermic” and
“endothermic.” Exothermic reactions release energy (which the universe
tends to like), while endothermic reactions consume energy (which the
universe tends to dislike). If, in the course of the reaction, the enthalpy
change is negative, the reaction is exothermic. If it’s positive, the reaction is
endothermic. That’s why (C) is correct.
- D Remember to always associate entropy with disorder. That’s what it
measures, and that’s why (D) is correct.
- F, T Divide and conquer! Look at the first statement on its own. Is it
true? No. The fact that a reaction is exothermic does not necessarily
mean that it’s spontaneous. The first statement is false.
Does the universe favor a negative enthalpy change?
Yes. Generally speaking, it likes exothermic reactions.
So the first statement is false, and the second is true.
- T, T, CE
Divide and conquer. Evaluate the first statement by
itself. Is it true or false? It’s true! In order for ice to
melt, it must absorb heat. Melting involves a net
absorption of heat energy because bonds between water
molecules must be broken in order for melting to occur;
it is an endothermic process.
What about statement II? Your own experience tells you
that this is true. Ice must absorb heat in order to melt.
Now put both statements together: ”Ice melting is an
endothermic process because heat must be absorbed by
ice if it is to melt.” Does it make sense? Absolutely. So
fill in the CE oval.
- C Starting with (A), let’s plug in choices. If the coefficient for O 2 is 1,
then there are two oxygen atoms on the left. Since we are starting with 3
oxygen atoms on the right, this number is too small. Try (B). If the
coefficient for O 2 is 2, we get 4 oxygen atoms on the left. Putting a 2 in
