- #1

Krokodrile

- 45

- 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 no-flow 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 what's 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*(T2-T1)

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*(T2-T1)

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 :).