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1. The problem statement, all variables and given/known data

When a system is taken from state i to state f along path iaf in Figure 18-41, Q = 60 cal and W = 20 cal. Along path ibf, Q = 51 cal.

Fig. 18-41 (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?

2. Relevant equations

[tex]\Delta E = Q - W[/tex] and is path independant

3. 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] 60-20+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 performedonthe system rather than work performedbythe system, I changed Q-W 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...

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# Homework Help: Thermodynamics-work, heat, & internal energy

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