Spontaneous Reactions and Molar Entropy

[Soaring Crane]

The reaction A(g) --> B(g) is spontaneous under standard conditions. Which of the following statements must be true?

I. B(g) --> A(g) is nonspontaneous under standard conditions.
II. A(g) will be completely converted to B(g) if sufficient time is allowed.
III. A(g) will be completely converted to B(g) rapidly.



a. none of these
b. I
c. I and II
d. I, II, and III




The speed of the reaction, or kinetics, is not used to define a spontaneous reaction, so III doesn't fit. It is I because
I is the reverse reaction, but I am not fully certain of II.



Which substance will have the highest standard molar entropy at 25 C ?
a. C(graphite)
b. C2H4(g)
c. CH3OH(l)
d. MgCO3(s)

Is it the only one in gas form since it has the most disorder?

Thank you.

 

[GCT]

1) II is also not true, can you tell me why? Think about the equilibrium Gibb's equation.

2)If it's a gas in standard conditions, yes.

 

[Blueshift5]

Yes, you are correct. The substance with the highest standard molar entropy at 25 C would be C2H4(g) because it is in the gaseous state, which has the most disorder and therefore the highest entropy. The other substances are in solid or liquid form, which have lower entropies.