Question

Assuming constant pressure, rank these reactions from most energy released by the system to most energy absorbed by the system, based on the following descriptions:

A. Surroundings get colder and the system decreases in volume.
B. Surroundings get hotter and the system expands in volume.
C.Surroundings get hotter and the system decreases in volume.
D. Surroundings get hotter and the system does not change in volume.
Also assume that the magnitude of the volume and temperature changes are similar among the reactions.
Rank from most energy released to most energy absorbed. To rank items as equivalent, overlap them.

Answer 1

Reaction B is the most exothermic as it releases energy and the surroundings get hotter. Reaction D is less exothermic as the surroundings get warmer without volume change. Reaction A is most endothermic, absorbing energy, indicated by cooler surroundings.

Step-by-step explanation:

Ranking the reactions from most energy released to most energy absorbed:

1. Exothermic reaction: Surroundings get hotter and the system expands in volume (B). This reaction releases the most energy, indicated by the heat given off to the surroundings.
2. Surroundings get hotter but volume doesn't change (D). This is still an exothermic reaction but less energy is released compared to B due to no work done on expansion.
3. Surroundings get hotter and the system decreases in volume (C). This describes an endothermic process where energy is absorbed, but because the surroundings get warmer, it's indicative of a net release of energy after accounting for the work done on the system (compression).
4. Endothermic reaction: Surroundings get colder and the system decreases in volume (A). This reaction absorbs the most energy, indicated by the surroundings getting colder.

In summary, the reactions involving the surroundings getting warmer are generally exothermic, while those involving the surroundings getting colder are endothermic. The volume change provides additional clues about energy changes; expansion suggests work is done by the system (releasing energy), while a decrease in volume suggests work is done on the system (absorbing energy).

Answer 2

B > D > C > A

Step-by-step explanation:

For the first law of the thermodynamics, the total energy variation in a process is:

ΔU = Q - W

Where Q is the heat, and W the work. If the system loses heat, Q < 0, if it absorbs heat, Q>0. If work is done in the system (volume decreases), W < 0, if the system does the work (volume increases), W > 0.

A. If the surroundings get colder, the system is absorbing heat, so Q>0, and the system decreases in volume so W < 0 :

ΔU = +Q - (-W) = +Q + W (absorbs a higher energy)

B. If the surroundings ger hotter, the system is losing heat, so Q<0, and the system expands, so W>0:

ΔU = -Q -W (loses higher energy)

C. Surroundings get hotter, Q<0, and the system decreases in volume, W<0

ΔU = - Q + W = 0 (magnitude of heat and work is similar)

D. Surroundings get hotter, Q<0, and the system is not changing in volume, W = 0.

ΔU = -Q (loses energy)

For the most released (more negative) for the most absorbed (most positive):

B > D > C > A