Which of the following results in the largest increase (most positive charge) in
ID: 911291 • Letter: W
Question
Which of the following results in the largest increase (most positive charge) in internal energy for a system?
a) The system volume decreases and the surroundings get colder.
b) The system volume increases and the surroundings get colder.
c) The system volume remails constant and the surroundings get colder.
d) the system volume increases and the surroundings get hotter.
e) The system volume increases and the surroundings get hotter.
2. When ammonium nitrate is dissolved in water, as shown in the equation below, the temperature of the water increases. What does this indicate about the solution process?
NH4NO3 (s) = NH4+ (aq) + NO3- (aq)
a) It is exothermic and dH is positive.
b) It is exothermic and dH is negative.
c) It is endothermic and dH is positive.
d) It is endothermic and dH is negative.
Explanation / Answer
1) Ans : (a)
Explanation
Change in internal energy dU = q + w q = heat gained or lost by the system
w = -nRT In(V2/V1)
a) The system volume decreases and the surroundings get colder.
surroundings get colder = heat gained by the system , so q = +ve
system volume decreases , w = +ve
b) The system volume increases and the surroundings get colder.
surroundings get colder = heat gained by the system , so q = +ve
system volume increases , w = -ve
c) The system volume remains constant and the surroundings get colder.
surroundings get colder = heat gained by the system , so q = +ve
system volume remains same, w = 0
d) The system volume increases and the surroundings get hotter.
surroundings get hotter = heat lost by the system , so q = -ve
system volume increases , w = -ve
e) The system volume increases and the surroundings get hotter.
surroundings get hotter = heat lost by the system , so q = -ve
system volume increases , w = -ve
There , system (a) has more positive change (+ve + +ve)
2) Ans : (b) - Exothermic and dH = -ve
Temperature of the water increases due to release of heat energy on dissolving NH4NO3 (s) in water.
This type of reaction is called exothermic reaction.
Heat eneegy released = Exothermic reaction
For exothermic reactions, dH = -ve
Therefore, answer is (b) i.e. Exothermic and dH = -ve
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