Lec 9 | MIT 5.60 Thermodynamics & Kinetics, Spring 2008

[naveenthumu8]

sign convention is really confusing......

[gomunkul]

He sound just like Christopher Walken !

[Andre1a]

:O thats what i call high quality (Y)

[moyamba5]

can somebody explain were he say W irrev is greater than W rev at 44:32

[panumbang]

Hi, great job. I just want to check one thing. at about 10mins, when he was talking about heat input (Q) = q1, where is q2? why it has not been taken into consideration? otherwise, excellent video for us to learn the concept.

[saiyeek]

He confuses me with the sign convention! -q2 is positive kind of thing. What is this?

[s27448632]

q2 is entering the cold reservoir thus its negative.

[PointOnACurve]

By convention, heat or work flowing into the system will be positive. In general, when you talk about q or w in thermodynamics with this convention, you are basicly only talking about the flow into the system. Now, with this convention, a heat flow out, designated by arrow leaving, will have q negative because heat is flowing out, and then -q will be positive. The "-" is there because the arrow is leaving the system;"-"means out in this case. It's for the heat balance around the engine: In-Out.

[nolaeast]

@PointOnACurve

FYI

By convention in thermodynamics, Work in is, -W, and Work out is +W. Where as, Heat in is , +Q and Heat out is -Q.

Thus the First Law equation gives;

Q - W = change in U.

Where U is the internal energy.