Understanding the definitions of heat and work

Question

A mixture of gaseous reactants is put in to a cylinder, where a chemical reaction turns them in to gaseous products. The cylinder has a piston that moves in or out as necessary to keep a constant pressure on the mixture of 1 atm. The cylinder is also submerged in a large insulated water bath.
From previous experiments, this chemical reaction is known to release 244. kJ of energy.
The temperature of the water bath is monitored, and it is determined from this data that 150. kJ of heat flows out of the system during the reaction.

1) is the reaction exothermic or endothermic?

2) Does the temperature of the water go up or down?
3) does the piston move in, out, or neither?
4)does The gas mixture do work, Or is work done on it?

5)how much work is done on (or by) the gas mixture?

Answer 1

(1)

 

Since the reaction releases heat, it is exothermic.

 

(2)

 

Unless you have an infinite reservoir of water, the water temperature should rise as heat flows into the water.  That is how you measure the heat flow into the water, by measuring the water's temperature rise, mass, and knowing its specific heat.

 

(3)

 

As the gas heats up, its pressure should rise, which in turn displaces the piston in the outward direction.  This is positive work, i.e. work being done by the system.

 

(4)

 

Since the piston moves out, the gas mixture does work on ts surroundings.

 

(5)

 

Do an energy balance.  If the system released 244 kJ of energy, by only 150 kJ went into the water, then the difference must be the work done by the system on its surroundings.

 

W = (244 - 150) kJ = ? kJ