Can you help me with this heat energy problem?

Question

As a system increases in volume, it absorbs 52.5J of energy in the form of heat from its surroundings. The piston is working against a pressure of 0.500 atm. The final volume of the system is 58.0 L. How do I calculate the inital energy of the system if the internal energy of the system decreased by 102.5 J?

Answer 1

Hi, no one answered this problem for you, so I will take a crack at it.  I think what you mean to do here is to calculate the initial volume of the system, V1.

 

Given deltaE=q+w, where deltaE=-102.5 J and q=+52.5 J, work (w) may be expressed as -P(V2-V1).  Putting it all together we have -102.5 J = +52.5 J + [-0.500 atm(58.0 L - V1)].  The change in energy for the system is -102.5 J.

 

=> -155 J = -29 atm*L + (0.500 atm)V1

=> convert J to atm*L => -155 J (atm*L/101.34 J) = -1.5295 atm*L

=> -1.5295 atm*L = -29 atm*L + (0.500 atm)V1

+27.4705 atm*L = (0.500 atm)V1

V1 = 54.9 L = initial volume