 #1
 486
 1
Thermodynamicswork, heat, & internal energy
When a system is taken from state i to state f along path iaf in Figure 1841, Q = 60 cal and W = 20 cal. Along path ibf, Q = 51 cal.
Fig. 1841 (see attatched)
(a) What is W along path ibf?
(b) If W = 13 cal for the return path fi, what is Q for this path?
(c) If E_int,i = 7 cal, what is Eint,f?
(d) If E_int,b = 18 cal what is Q for path ib?
(e) For the same value of E_int,b, what is Q for path bf?
[tex]\Delta E = Q  W[/tex] and is path independant
(a) [tex]\Delta E_{iaf} = \Delta E_{ibf}[/tex]
hereon, iaf will be abbreviated a, and ibf will be abbreviated b.
[tex] Q_a  W_a = Q_b  W_b[/tex]
[tex] Q_a  W_b + Q_b = W_b [/tex]
[tex] 6020+51=W_b=91[/tex]
So W_b = 91 cal. Wrong. And yes the problem wants the answer in calories.
On the chance that they're giving work performed on the system rather than work performed by the system, I changed QW to Q+W, and got that W_b=29 cal, which is still wrong.
I used the same exact reasoning for part b (and got it wrong).
I got part C correct [47 cal] using the fact that DeltaE is path independent, and Delta E = final energy  initial energy.
Parts d and e I just have no idea where to begin. So I guessed 18 cal for both. Surprise! Both wrong...
Homework Statement
When a system is taken from state i to state f along path iaf in Figure 1841, Q = 60 cal and W = 20 cal. Along path ibf, Q = 51 cal.
Fig. 1841 (see attatched)
(a) What is W along path ibf?
(b) If W = 13 cal for the return path fi, what is Q for this path?
(c) If E_int,i = 7 cal, what is Eint,f?
(d) If E_int,b = 18 cal what is Q for path ib?
(e) For the same value of E_int,b, what is Q for path bf?
Homework Equations
[tex]\Delta E = Q  W[/tex] and is path independant
The Attempt at a Solution
(a) [tex]\Delta E_{iaf} = \Delta E_{ibf}[/tex]
hereon, iaf will be abbreviated a, and ibf will be abbreviated b.
[tex] Q_a  W_a = Q_b  W_b[/tex]
[tex] Q_a  W_b + Q_b = W_b [/tex]
[tex] 6020+51=W_b=91[/tex]
So W_b = 91 cal. Wrong. And yes the problem wants the answer in calories.
On the chance that they're giving work performed on the system rather than work performed by the system, I changed QW to Q+W, and got that W_b=29 cal, which is still wrong.
I used the same exact reasoning for part b (and got it wrong).
I got part C correct [47 cal] using the fact that DeltaE is path independent, and Delta E = final energy  initial energy.
Parts d and e I just have no idea where to begin. So I guessed 18 cal for both. Surprise! Both wrong...
Attachments

2.2 KB Views: 592