Cyclic thermodynamics processes

In summary, the conversation discusses whether or not ΔH=q in a cyclic process involving a gas where the pressure varies but returns to the original value at the end. The participants also discuss the definition of a state function and how it relates to a change in heat (q). Ultimately, they conclude that in a cyclic process, ΔH is equal to 0 and it is unclear if q is also equal to 0.
  • #1
Bipolarity
776
2

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 [itex]ΔH=q[/itex]

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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  • #2
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
 
  • #3
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 [itex]ΔH [/itex] must be 0. But what about the heat? Must it also be 0?

BiP
 
  • #4
Bipolarity said:
So the state of the system has not changed, so the [itex]ΔH [/itex] 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
 
  • #5
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 [itex] ΔH=q [/itex] ? How can you assume it to be true if you haven't shown it to be true?

BiP
 
  • #6
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
 
Last edited:

FAQ: Cyclic thermodynamics processes

What is a cyclic thermodynamic process?

A cyclic thermodynamic process is a series of thermodynamic changes that start and end at the same state, resulting in a closed loop on a thermodynamic diagram. This means that the system returns to its initial state after completing a full cycle.

What is the first law of thermodynamics in relation to cyclic processes?

The first law of thermodynamics states that energy cannot be created or destroyed, but can only be transferred or converted from one form to another. In the case of cyclic thermodynamic processes, this means that the net change in energy of the system over a full cycle must be zero.

What is the difference between a reversible and irreversible cyclic process?

A reversible cyclic process is one in which the system can be brought back to its initial state by reversing each step of the process while maintaining equilibrium with its surroundings. An irreversible cyclic process, on the other hand, cannot be reversed and results in a net change in the system's energy and/or entropy.

How are cyclic thermodynamic processes used in practical applications?

Cyclic thermodynamic processes are used in a variety of practical applications, such as in the operation of heat engines (e.g. car engines) and refrigeration systems. They are also important in the study of chemical reactions and the design of industrial processes.

What is the Carnot cycle and how does it relate to cyclic thermodynamics?

The Carnot cycle is a theoretical thermodynamic cycle that consists of four reversible processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression. It serves as an idealized model for a heat engine and is used to define the maximum efficiency that any heat engine operating between two temperatures can achieve. The Carnot cycle is an important concept in cyclic thermodynamics as it helps to understand the limitations of real-world thermodynamic processes.

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