If a particular reaction evolves 192 kJ of heat while expanding from 1.00 L to 2.00 L at 125 atm of pressure, what is the overall energy change for the system?
q = -192 kJ since that is evolving heat.
w = pdV = 125*(2) an that is - since it is expanding; i.e., it is doing work against the atmosphere while expanding.
Note that w is in L*atm and need to be changed to J. Do that by x 101.325 then convert to kJ.
Note: work is given in texts as -pdV and then dV is V2-V2 so this would be = -pdV = -125 atm x (2.00-1.00) = - etc etc.
I don't do that. I just remember work is pdV, calculate a number, then assign a + or - to it based on if the system is doing work of if it is having work done on it. I do that because this way I don't need to differentiate between V2 and V1.