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 3
 Homework Statement:
 8 pounds of a gas with cp = 0.25 btu/lbm(ºF) and cv = 0.18 btu/lbm(ºF) that is at 100 ºF, is placed in a piston cylinder and 500 btu is delivered as heat in a noflow process at constant pressure. Determine the final temperature, the internal energy change, and the work done
 Relevant Equations:

Q=m*C*△T
W = △U + Q
So, the Cp and Cv its very confusing for me. But, i understand whats its happening in this process, so, i use the logic and first i obtain a ecuation for obtain the final temperature ecuaticon:
Q=m*C*△T
Q=m*C*(T2T1)
T2=(Q+T1)/(m*C)
If the process its in constant pressure, i use the Cp valor:
T2=(500 +100ºF)/(8 pounds * 0.25btu/lbm(ºF)
T2 = 300 ºF
So, i determinate the internal energy change using this ecuacion:
△U= 36 Cv*△T
△U = 0.18 btu/lbm(ºF) * (300 ºF  100 ºF)
△U = 36 btu/lbm(ºF)
For the work:
W = △U + Q
W = 36 btu/lbm(ºF) `+ 500 btu
W = 536
I know that my results its incorrect, but these "Cp and Cv" confusing to me.
I need some help please :).
Q=m*C*△T
Q=m*C*(T2T1)
T2=(Q+T1)/(m*C)
If the process its in constant pressure, i use the Cp valor:
T2=(500 +100ºF)/(8 pounds * 0.25btu/lbm(ºF)
T2 = 300 ºF
So, i determinate the internal energy change using this ecuacion:
△U= 36 Cv*△T
△U = 0.18 btu/lbm(ºF) * (300 ºF  100 ºF)
△U = 36 btu/lbm(ºF)
For the work:
W = △U + Q
W = 36 btu/lbm(ºF) `+ 500 btu
W = 536
I know that my results its incorrect, but these "Cp and Cv" confusing to me.
I need some help please :).