Consider these changes. (a) Hg(l)->Hg(g) (b) 3O2(g)->2O3(g) (c) CuSo4*5H2O(s)->CuSO4(s)+5H2O(g) (d) H2(g)+F2(g)->2HF(g) At constant pressure, in which of the reactions is work done by the system on the surroundings? By the surroundings on the system? In which of them is no work done?
a and c more gas on product side so system expands and P*delta V is done on surrounding.
b fewer moles on right than left so system contracts and p*delta V is done by surroundings.
d no change in volume so no work done.
A: "Oh, Hg(l) turning into Hg(g) is like liquid mercury becoming a gas. That's quite a transformation! In this reaction, work is done by the system on the surroundings."
B: "Ah, here we have oxygen gas converting to ozone gas. O3, the fancy version of O2! In this reaction, no work is done by either the system or the surroundings. It's a lazy one!"
C: "Ah, the copper sulfate pentahydrate losing some water to become copper sulfate. Hydration is not on the menu anymore! And hey, water vapor! In this reaction, work is done by the surroundings on the system. The system just sits back and lets the surroundings do the work."
D: "Ah, here we have hydrogen gas having a fiery fling with fluorine gas. A match made in science heaven! In this reaction, work is done by the surroundings on the system. The surroundings are like, 'Hey, H2 and F2, you crank up that heat!'"
To summarize:
- In reaction A, work is done by the system on the surroundings.
- In reaction B, no work is done by either the system or the surroundings.
- In reaction C, work is done by the surroundings on the system.
- In reaction D, work is done by the surroundings on the system.
To determine in which reactions work is done by the system on the surroundings, by the surroundings on the system, and in which no work is done, we need to examine the change in volume for each reaction.
(a) Hg(l) -> Hg(g):
In this reaction, the liquid mercury (Hg) is converting into gaseous mercury. This expansion of the system against atmospheric pressure means work is done by the system on the surroundings.
(b) 3O2(g) -> 2O3(g):
This reaction involves the conversion of three molecules of oxygen gas (O2) into two molecules of ozone gas (O3). There is no change in volume since the number of moles of gas remains the same. Therefore, no work is done by either the system or the surroundings.
(c) CuSO4·5H2O(s) -> CuSO4(s) + 5H2O(g):
In this reaction, solid copper sulfate pentahydrate (CuSO4·5H2O) is decomposing into solid copper sulfate (CuSO4) and gaseous water (H2O). As water vapor is released into the surroundings, the system expands, and work is done by the system on the surroundings.
(d) H2(g) + F2(g) -> 2HF(g):
The reaction involves the combination of hydrogen gas (H2) and fluorine gas (F2) to form hydrogen fluoride gas (HF). Again, no change in volume occurs, so no work is done by either the system or the surroundings.
In summary:
- Work is done by the system on the surroundings in reactions (a) and (c).
- No work is done in reactions (b) and (d).
To determine whether work is done by the system on the surroundings, by the surroundings on the system, or if no work is done, we need to consider the changes in volume and the pressure in each reaction.
The general equation for work done is given by:
Work = -PΔV
where P is the pressure and ΔV is the change in volume.
Now let's analyze each reaction:
(a) Hg(l) → Hg(g)
In this reaction, the system transitions from a liquid to a gas. As the volume increases during this phase change, work is done by the system on the surroundings.
(b) 3O2(g) → 2O3(g)
This reaction does not involve any change in volume. Therefore, no work is done.
(c) CuSO4*5H2O(s) → CuSO4(s) + 5H2O(g)
In this reaction, the solid CuSO4·5H2O decomposes into the solid CuSO4 and gaseous water (H2O). As there is an increase in volume due to the formation of gaseous water, work is done by the system on the surroundings.
(d) H2(g) + F2(g) → 2HF(g)
This reaction involves the chemical reaction between hydrogen gas (H2) and fluorine gas (F2) to form hydrogen fluoride (HF) gas. While there might be a change in volume due to the reaction, in this case, we cannot determine the direction of work without additional information, such as the pressure and volume conditions.
In summary:
- Work is done by the system on the surroundings in reaction (a) and reaction (c).
- No work is done in reaction (b).
- The direction of work done in reaction (d) cannot be determined without additional information.
Please note that the analysis above assumes constant pressure conditions.