Pressure/Introductory Thermodynamics

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SUMMARY

The discussion focuses on calculating the work done (w) during a chemical reaction involving a piston in a container with a cross-sectional area of 100 cm² and an external pressure of 567 torr. The correct formula for work is w = - (Pressure)(Change in Volume), where the pressure must be converted to Pascals (Pa). The calculated work, disregarding the sign, is 151.188 J, but the sign is crucial as it indicates the direction of work done by the system. The correct answer must reflect the negative sign due to the expansion against external pressure.

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  • Understanding of basic thermodynamics concepts
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  • Study the implications of sign conventions in thermodynamics
  • Learn about the relationship between pressure, volume, and work in gas systems
  • Explore the concept of internal energy changes during chemical reactions
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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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