At constant pressure, which of these systems do work on the surroundings? Check all that apply?

Home Work Help
,
1

At constant pressure, which of these systems do work on the surroundings? Check all that apply.

  1. 2A(g)+B(g)–>4C(g)
  2. 2A(g)+2B(g)–>3C(g)
  3. A(s)+2B(g)–>2C(g)
  4. 2A(g)+B(s)–>3C(g)

Answer:

Work done = pressure x change in volume
So, imagine reactant A(g) and B(g) were allowed to react to form product C(g) in a closed cylinder with a piston at constant pressure. If the volume of the product is greater than the reactants’ the piston will move against the atmospheric pressure and the work will be done by the product in the cylinder.
If on the other hand, if there is a decrease in product volume, then the atmosphere will push the piston into the cylinder and the atmosphere will do work on the piston - or negative work will be done by the piston.
So, in…

  1. A(g) + B(g) --> C(g) - no work done by system
  2. A(s) + B(g) --> 2C(g) - work done by system
  3. A(g) + B(g) --> 3C(g) - work done by system
  4. 2A(g) + B(g) --> C(g) - no work done by system