Out of my First Law of Thermodynamics problem set for practice, I am unable to solve one of the problems given to me. I'd like some direction on where to proceed, since I am a bit lost with the problem. It reads:
A 15.0 g piece of Mg(s) is deposited in a container with HCl(aq). Calculate the work done by the system as a consequence of the reaction, if Patm = 1.1 atm and T = 298.15 K. Presume ideal behavior.
The reaction I calculated was: Mg(s) + 2 HCl(aq) --> H2(g) + MgCl2(aq)
Thus far, we've covered (and which are stuff I may be able to relate)
dW = -Pext dV (ext in this case, since the process is highly irreversible)
dU = dQ + dW
H = U + PV
I am assuming that the container will be open to the environment, and that thus the external pressure will be constant, making the process isobaric. However, I have doubts on how to calculate the initial volume of the system, or if my reasoning is correct at all.
I really don't want answers on how to do it, I just need tugs in the right direction to begin thinking on how to solve the problem.