How Does Heat Relate to Work in Thermodynamics?

[Pushoam]

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Assuming that by the word "Work", work on the system is meant.
Both heat and work is energy in transit.
I think heat is work done by constituent particles of a system on another system in contact.
Now the work done by us on a system gets transformed into the K.E. and P.E. of the system.
In thermodynamics, here it is assumed that the change in the P.E. is 0. So, work done by us is nonthing but the change in the K.E. of the system.
This change in the K.E. of the system is nothing but the change in the average K.E. of the constituent particles of the system. Now this change in the average kinetic energy of the constituent particles is nothing but the work done on the constituent particles , hence, heat.

Is this right?

 

[sophiecentaur]

Have you Googled for definitions of 'Heat'?

 

[Andrew Mason]

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View attachment 212198
Assuming that by the word "Work", work on the system is meant.
Both heat and work is energy in transit.
I think heat is work done by constituent particles of a system on another system in contact.
Now the work done by us on a system gets transformed into the K.E. and P.E. of the system.
In thermodynamics, here it is assumed that the change in the P.E. is 0. So, work done by us is nonthing but the change in the K.E. of the system.

There is no such assumption. Internal energy can consist of kinetic and potential energy.

This change in the K.E. of the system is nothing but the change in the average K.E. of the constituent particles of the system. Now this change in the average kinetic energy of the constituent particles is nothing but the work done on the constituent particles , hence, heat.

This is not what the first law says. It says that heat flow into the system plus the mechanical work done on the system is equal to the the change in internal energy of the system. In thermodynamics we distingush between microscopic work that is randomly done on by molcules by or on other molecules (Q) and useful macroscopic work done on or by systems (W).

AM

 

[Pushoam]

Thank you for the reply.
Heat is energy in transit.
I am studying thermodynamics by Blundell and Blundell.

 

[Pushoam]

. In thermodynamics we distingush between microscopic work that is randomly done on by molcules by or on other molecules (Q) and useful macroscopic work done on or by systems (W).

So, heat is nothing but another name for the microscopic work. Right?

 

[Andrew Mason]

So, heat is nothing but another name for the microscopic work. Right?

If you define work as a force applied over a distance and if you are dealing only with discrete particles randomly applying forces to other discrete particles over microscopic distances, then heat flow can be thought of as that kind of work But there are other means by which heat flow can occur, such as radiation. In thermodynamics we use heat flow to refer to all types of energy transfer other than useful macroscopic mechanical work done by, or on, systems.

AM

 

[Pushoam]

If you define work as a force applied over a distance and if you are dealing only with discrete particles applying forces to other discrete particles over microscopic distances, then hsat flow can be thought of as that kind of work But there are other means by which heat flow can occur, such as radiation. in thermodynamics we use heat flow to refrer to all types of energy transfer other than useful macroscopic mechanical work done by or on systems.

AM

So, this means depending on the process, sometimes heat could be microscopic work, sometimes it could be radiation, sometimes something else.
Here, in the question , heat is microscopic work. Right?

 

[Andrew Mason]

So, this means depending on the process, sometimes heat could be microscopic work, sometimes it could be radiation, sometimes something else.
Here, in the question , heat is microscopic work. Right?

I would not use the term "microscopic work". Thermodynamics is confusing enough as it is. Work, in thermodynamics, means mechanical, macroscopic work done by a system. Besides, not all random energy transfers to molecules fit the normal definition of work: $W = \int \vec{F}\cdot\vec{d}$. For example, photon absorption by an atom is a quantum mechanical event. The photon does not really apply a force to an atom over a distance when it is absorbed by the atom. But that atom's internal energy increases.

Heat, or heat flow (which is a better term, in my opinion), has a particular meaning in thermodynamics. If a system and its surroundings are initially in equilibrium states and undergo a process resulting in new equilibrium states, the first law will tell you the relationship between the heat flow that occurred during that process, the work done by the system during the process, and the change in internal energy of the system between initial and final states:
Q = ΔU + W
where Q is the heat flow (into the system), W is the mechanical work done BY the system and ΔU is the change in internal energy of the system. That is the best way to define heat flow: it is an energy transfer to the system that is the sum of the system's change in internal energy + the work done BY the system.

AM

 

[Pushoam]

Thank you.