posted by Yasha .
At constant pressure, which of these systems do work on the surroundings? Check all that apply.
A(s) + 2B(g) ---> C(g)
2A(g) + B(g) ---> 4C(g)
A(g) + 2B(g) ---> 2C(g)
A(s) + B(s) ---> C(g)
If # mol gets larger, that's an expansion, and the system does work on the surroundings. If # mol gets smaller, that's a decrease in volume, and the surroundings do work on the system.
Watch out for those solids. They are not gases and don't count when counting moles.
Thank you so very much~! <3