There is two practice problems which I don't really get. I will just jump right to it.
Practice problem number 1 Which of these spontaneous procecces below are:
2)
Magnesium bonds burnsa) exothermic and leads to an increase in entropy in the system
b) exothermic and leads to a decrease in entropy in the system
c) endothermic and leads to an increase in entropy in the system
d) Neither exothermic nor endothermic, but leads to an increase in entropy in the system
I figured that the answer had to be b) based on elimination; I also checked it with the answer from the student book. However, I don't understand how you can see that the reaction is «exothermic and leads to a decrease in entropy in the system» based on the text. Can anybody please clarify this for me?
Practice problem number 2 Show with calculations if this reaction goes spontaneously at room temperature (25oC)
2Al(s) + 3Cl(g)
2AlCl
3(s)
ΔHf(AlCl3(s)) = -706 kj/mol
S(Al(s)) = 28,0 j/(mol * K)
S(cl
2(g)) = 223 j/(mol * K)
S(AlCl
3(s)) = 109 j/(mol * K)
After some calculations, I got:
ΔG = -1412 kj -(298K * (-0.507 kj/K)) = -1260,1 kj
The process goes spontaneously at room temperature.
However the answer in my student book was: - 1560 kj, and I was wondering if the book itself had made a mistake?