Achieve week 3/4 #13

[Emily Hou 1H]

At constant pressure, which of these systems do work on the surroundings?
2A(g)+2B(g)⟶3C(g)

2A(g)+B(s)⟶3C(g)

A(g)+B(g)⟶C(g)

A(g)+B(g)⟶3C(g)

How do you tell which system is doing work on the surroundings based on the reactions?

[Xuan Lai 1H]

You can tell a system is doing work on its surroundings if it produces more mols than it consumes. For example:
2A(g)+2B(g)⟶3C(g)
4 mols --> 3 mols, so you can eliminate this one.
Also, it is important to note the phases they are in like in:
2A(g)+B(s)⟶3C(g)
B is a solid so it is not counted (2mols --> 3mols)
Using the same strategy, you will find two correct options, hope this helps!

[Kathleen Wijaya 3L]

Additionally, a system does work on surroundings if it produces more moles of gas than it consumes. Thus, work is also negative because in this situation under constant pressure, deltaV and deltaN are both positive.

[Rio Gagnon 1G]

If there are more moles in the products than the reactants, that means that the value for work is negative. This means the system is doing work on its surroundings.