Answer
Gas expanding or compressing depends on the mole difference between product and reactants. Only gas can do PV work. Liquids and solids cannot.
a) $\Delta$ n = 1 mol -> Expanding -> Work done by system
b) $\Delta$ n = -1 mol -> Compressing -> Work done by surroundings
a) $\Delta$ n = 5 mol -> Expanding -> Work done by system
a) $\Delta$ n = 0 mol ->No work done
Work Step by Step
Gas expanding or compressing depends on the mole difference between product and reactants. Only gas can do PV work. Liquids and solids cannot.
a) $\Delta$ n = 1 mol -> Expanding -> Work done by system
b) $\Delta$ n = -1 mol -> Compressing -> Work done by surroundings
a) $\Delta$ n = 5 mol -> Expanding -> Work done by system
a) $\Delta$ n = 0 mol ->No work done