At constant pressure, which of these systems do work on the surroundings?
A(s)+B(s)-->C(g)
2A(g)+2B(g)--> 3C(g)
A(g)+B(g)-->3C(g)
2A(g)+3B(g)-->4C(g)
I've tried everything and I just don't understand what I'm doing wrong.
So why not tell us what you did? That way we could help. This way you just want the answer.
To determine which of these systems do work on the surroundings at constant pressure, we need to examine the change in the number of moles of gas in the reaction.
Remember that for a gas, work can be done by expansion or compression. If the number of moles of gas increases during a reaction, it means that the system does work on the surroundings. Conversely, if the number of moles of gas decreases, the surroundings do work on the system.
Let's analyze each reaction one by one:
A(s) + B(s) --> C(g)
There are no gaseous reactants or products in this reaction, so no work is done on the surroundings.
2A(g) + 2B(g) --> 3C(g)
In this reaction, the number of moles of gas increases from 4 moles (2A + 2B) to 6 moles (3C). Therefore, the system does work on the surroundings.
A(g) + B(g) --> 3C(g)
Here, the number of moles of gas remains the same before and after the reaction (2 moles), so no work is done on the surroundings.
2A(g) + 3B(g) --> 4C(g)
In this reaction, the number of moles of gas decreases from 5 moles (2A + 3B) to 4 moles (4C). As a result, the surroundings do work on the system.
So, out of the four reactions, the systems that do work on the surroundings at constant pressure are:
- 2A(g) + 2B(g) --> 3C(g)
- 2A(g) + 3B(g) --> 4C(g)
Make sure you double-check your calculations to ensure that you have taken the correct number of moles of each substance into account.