Work and Heat Flow of a Heat Engine Cycle

[ally1h]

Homework Statement

A heat engine follows the cycle shown in the figure. a) How much net work is done by the engine in one cycle? b) what is the heat flow into the engine per cycle?

Diagram:
http://farm4.static.flickr.com/3050/2703330973_26acb35c27.jpg?v=0

Homework Equations

W = -PΔV
ΔU = Q+W

The Attempt at a Solution

a)
W = -PΔV
W = (-3.00 atm)(0.600 m^3)
W = -1.8 J

b)
ΔU = Q+W
ΔU = 0, due to energy conservation
so...
0 = Q+W
Q = W
Q = 1.8




Everything look okay? I wasn't so sure about part b...

 

[Irid]

Probably in part (b) the question asks for total heat added to the engine per one cycle, not the net heat gained (i.e. not [added]-[removed]). So, you should decide which part of the cycle corresponds to heating and then use

$$dQ = p\, dV + V\, dp$$

to calculate the heat.

 

[yellowgators]

The Attempt at a Solution

a)
W = -PΔV
W = (-3.00 atm)(0.600 m^3)
W = -1.8 J

Your pressure needs to be converted into Pa to get the right units.