Chemistry

I would really like to understand how to do these problems, because my exam is coming up in a few weeks. I still cannot comprehend how you can tell if a system is is positive or negative according to reaction.

For #1, I presume it is E if it is spontaneous at all temperatures. For #2, I think ΔS have to be negative since the reaction contains all gas phases. But I have no idea if you can tell if ΔH is spontaneous or nonspontaneous..And for #3, I presume it is A(?) basing on Gibbs Free Energy.

1. 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) ΔG is positive at all temperatures.
B) ΔG is positive and ΔS is positive.
C) ΔH is negative and ΔS is negative.
D) ΔH is negative and ΔS is positive.
E) ΔH is positive and ΔS is negative.

2. Consider the following reaction:

C3H8(g) + 5O2(g) ---> 3CO2(g) + 4H2O(g)

One would predict that

A) ΔH is positive and ΔS is positive for the reaction.
B) ΔH is negative and ΔS is negative for the reaction.
C) ΔH is negative and ΔS is positive for the reaction.
D) ΔH is positive and ΔS is negative for the reaction.
E) ΔG is positive at all temperatures.

3. For the reaction system that is at equilibrium, which of the following must always be true?

A) ΔG = 0
B) ΔH = 0
C) ΔU = 0
D) ΔS = 0
E) q = 0

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  1. Did you read my response to your earlier post with this same question? If not you should go back to read it. If so, then please go through and explain, in detail, exactly what you don't understand about my answers. If I answer this post I'll just rewrite what I've already written earlier.

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