- #1
cookiemnstr510510
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- Homework Statement
- Consider the reaction between zinc and hydrochloric acid as it takes place in a nearly evacuated, insulated container attached to a piston-cylinder assembly. When this reaction happens the piston moves up slightly due to the chemical reaction. Is the work positive or negative? Take the Zinc and hydrochloric acid as the system.
- Relevant Equations
- conventions?
I am a bit confused on the definition/convention of work. In some books I see statements that say :
"If work is done on the system, its sign is positive. If work is done by the system, its sign is negative."
And in other books I see things like:
"By convention, work is regarded as positive when the displacement is in the same direction as the applied force and negative when they are in opposite directions."
Since the system is the zinc and HCl and the piston moves then work is being done BY the system so work would be negative (according to the first quoted statement).
But if I look at the second quoted statement above I get a bit confused, is the "Applied Force" coming from the chemical reaction? If so then the force and displacement are in the same direction and work should be negative.
Or is the point that some books use one convention and other books use the other?
I would like to make sure that in this example the "Applied Force" is coming from the chemical reaction. I guess another possibility is the "Applied Force" is coming from the surroundings holding the piston in place with whatever atmospheric pressure it is applying to the system.
Thanks!
"If work is done on the system, its sign is positive. If work is done by the system, its sign is negative."
And in other books I see things like:
"By convention, work is regarded as positive when the displacement is in the same direction as the applied force and negative when they are in opposite directions."
Since the system is the zinc and HCl and the piston moves then work is being done BY the system so work would be negative (according to the first quoted statement).
But if I look at the second quoted statement above I get a bit confused, is the "Applied Force" coming from the chemical reaction? If so then the force and displacement are in the same direction and work should be negative.
Or is the point that some books use one convention and other books use the other?
I would like to make sure that in this example the "Applied Force" is coming from the chemical reaction. I guess another possibility is the "Applied Force" is coming from the surroundings holding the piston in place with whatever atmospheric pressure it is applying to the system.
Thanks!