A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The cylinder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of . The cylinder is also submerged in a large insulated water bath. (See sketch at right.) From previous experiments, this chemical reaction is known to release of energy. The position of the piston is monitored, and it is determined from this data "that the piston does of work on the system" during the reaction. Required:
a. Is the reaction exothermic or endothermic?
b. Does the temperature of the water go up or down?
c. Does the piston move in, out, or neither?
d. Does The gas mixture do work, Or is work done on it?
e. How much work is done on (or by) the gas mixture?

a) The reaction is exothermic

b) The temperature of the water goes up

c) The piston move in

d) Work is done on the gas mixture

e) The amount of work done on the gas mixture is given as

W = PΔV

where

W is the work done on the gas mixture

P is the pressure within the cylinder after the reaction

ΔV is the change (a decrease) in volume of the gas mixture

Explanation:

a) Since the chemical reaction is known to release energy into the surrounding, then it is an exothermic reaction.

b) Sine the reaction releases energy into the water, the energy of the water will go up, causing the temperature of the water to go up.

c) The piston will move in, since it was determined from data that the piston does work on the system. When the piston moves in work is done on the system.

d) Work is done on the gas mixture, because the piston moves in, compressing the gas.

e) From basic thermodynamics, we know that when work is done a system, then it means the system is compressed, and the equation for the work done on a system is given as

W = PΔV

where

P is the pressure withing the cylinder

ΔV is the change in the volume of the system. The volume of the system decreases, and hence the work done will be negative.