Cyclic thermodynamics processes

AI Thread Summary
In a cyclic thermodynamic process, the change in enthalpy (ΔH) is zero since the system returns to its original state. The discussion centers on whether the heat transfer (q) can also be considered zero, given that ΔH equals q. Participants emphasize that while ΔH is a state function and equals zero, q is a path function and may not necessarily be zero. The conclusion drawn is that ΔH=q does not hold true without further justification, as q can vary depending on the specific path taken during the process. Overall, the relationship between ΔH and q in cyclic processes requires careful consideration of their definitions and properties.
Bipolarity
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Homework Statement


Consider a cyclic process involving a gas. If the pressure of the gas varies during the process but returns to the original value at the end, is it correct to write ΔH=q

Homework Equations





The Attempt at a Solution


I'm actually not sure. q is a path function and H is a state function. To be honest I have no idea how to approach this problem, perhaps someone can give me a small hint.

BiP
 
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How is a state of a gas defined? What is a state function?
Suppose you have a function F(x,y,z) and F(1,2,3)=10 and then you let the variables change, but they return to the original values (1,2,3), what will be F(1,2,3)?

ehild
 
ehild said:
How is a state of a gas defined? What is a state function?
Suppose you have a function F(x,y,z) and F(1,2,3)=10 and then you let the variables change, but they return to the original values (1,2,3), what will be F(1,2,3)?

ehild

So the state of the system has not changed, so the ΔH must be 0. But what about the heat? Must it also be 0?

BiP
 
Bipolarity said:
So the state of the system has not changed, so the ΔH must be 0. But what about the heat? Must it also be 0?

BiP

If ΔH=q and ΔH=0 then what else can q be?

ehild
 
ehild said:
If ΔH=q and ΔH=0 then what else can q be?

ehild

I'm sorry but I am not sure you read the OP. The question asked whether or not ΔH=q ? How can you assume it to be true if you haven't shown it to be true?

BiP
 
You know that ΔH=0 in a cyclic process. Now you need to look after what q and ΔH are, and find out if the equation ΔH=q holds.

ehild
 
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