Work and Heat Flow of a Heat Engine Cycle

AI Thread Summary
The discussion focuses on calculating the net work done by a heat engine and the heat flow into the engine during one cycle. The initial calculations show that the net work done is -1.8 J, derived from the formula W = -PΔV. However, there is a clarification needed regarding the heat flow, as it should reflect the total heat added rather than the net heat change. The correct approach involves identifying the heating phase of the cycle and using the appropriate equations, emphasizing the need to convert pressure into Pascals for accurate results. Overall, the calculations require adjustments to ensure accuracy in both work and heat flow assessments.
ally1h
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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...
 
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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.
 
ally1h said:

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.
 

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