Pressure/Introductory Thermodynamics

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AI Thread Summary
The discussion revolves around calculating the work done (w) in a chemical reaction involving a piston. The user correctly converts the pressure from torr to pascals and calculates the change in volume based on the piston’s movement. However, the user overlooks the importance of the sign in the work equation, which indicates that work done by the system should be negative. The correct calculation should reflect this sign, leading to a final answer of -151.188 J. The conversation highlights the necessity of considering the sign in thermodynamic calculations.
JamesL
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Not sure what I am doing wrong...

Homework Statement


A chemical reaction takes place in a container
of cross-sectional area 100 cm2. As a result of
the reaction, a piston is pushed out through 20
cm against an external pressure of 567 torr.
What is the value for w for this reaction?
(Sign does matter.) Answer in units of J.

Homework Equations



w = - (Pressure)(Change in Volume)


The Attempt at a Solution



Cross sectional area = 100 cm^2 = .01 m^2
Change is piston distance = 20cm = .2 m

Pressure = 567 torr x 133.322 = 75593.574 Pa


Solution disregarding sign = [75593.574 kg/(m*s^2)][.01 m^2][.2 m]

---> 151.188 J

However this is coming up as incorrect.
 
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Looks OK to me. Why are you ignoring the sign when it says "sign does matter"?
 
Doc Al said:
Looks OK to me. Why are you ignoring the sign when it says "sign does matter"?

This is why a separate set of eyes is always helpful!
 
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