[EX5TASY]

Hey guys, can someone help explain this for me?

Consider a mixture of air and gasoline vapor in a cylinder with a piston. The original volume is 30. cm³. If the combustion of this mixture releases 1367. J of energy, to what volume will the gases expand against a constant pressure of 670. torr if all the energy of combustion is converted into work to push back the piston?

I'm trying to see if I'm understanding this correctly...I use this equation

w= -P?V


Since they say the combustion is converted into work,
1367J = -0.8815atm?V?

Then I convert that to J/L(atm), by multiplying 101.3J/L(atm) to get -15.3 as ?V?

That should be -15.3mL because it said 30.cm³ as the original volume.

Is any of that correct? 

[Yggdrasil]

w is defined as work done on the gas by the surroundings.  Since the system is losing energy by expanding, w = -1367J.

But, the number you get for ?V is correct (although the sign is incorrect).  ?V = 15.3mL.  Remember that ?V = V_final - V_initial.  So, since the initial volume is 30mL, the final volume V_final = ?V + V_initial = 45.3mL.

[EX5TASY]

Ah.,, i see now. I think I still did something wrong though, becuase the answer that we get is wrong.

When I multiply -1367J/-0.8815atm by 1L(atm)/101.3J, it comes out to 15.3 LITERS. So therefore, I should take the 30mL (because 30.cm3 is the original volume), and that is equal to 0.3L. So then,

Initial+Change= Final
0.3L + 15.3L = 15.6L

Does this answer make sense? I only have one submission left over for my online homework, so I want to make sure.

[Yggdrasil]

Ah, I didn't catch that.  But, I can catch your mistake here:  30mL is not 0.3L.  30mL is 0.03L

[EX5TASY]

Thanks!