# 1st law of thermodynamics

• curious bishal
In summary, in the process of proving the 1st law of thermodynamics, a system with initial energy E1 is supplied with heat q and some of it is used to do work. The final energy of the system, E2, is calculated as E2=E1+q+w where w is the work done. This may cause confusion because w can represent both work done on the system and work done by the system, resulting in different energy changes. However, the net energy change is always q-w, and the work is not double-counted.

#### curious bishal

On the way to prove 1st law of thermodynamics, you consider a system having initial energy E1. Then, you supply heat q to the system. Some part of the applied heat is used for doing work.
Then, again you consider the final energy (E2) of the system to be:
E2=E1+q+w
where w is the work done.

We all very well know that the work is done by the heat applied. If we add both heat applied and work done to the final energy, isn't the work done counted twice. I mean to say that the heat energy wasted in the work done is also consisted in q so why is there need to add w in the final energy E2.

I think the confusion here comes from whether w is the work done on the system, or the work done by the system. These change the energy by opposite amounts.

If the system is doing work w, the energy of the system decreases by w, so

E2=E1+q-w

Then, if q=w,
E2=E1

jfizzix said:
I think the confusion here comes from whether w is the work done on the system, or the work done by the system. These change the energy by opposite amounts.

If the system is doing work w, the energy of the system decreases by w, so

E2=E1+q-w

Then, if q=w,
E2=E1
It doesn't give the solution to my problem. Why is the work done counted double?

The work is not double-counted.

If the system starts at energy E1, and you add heat q to it, the energy has changed to amount E1'= E1+q.

If the system then performs work w on its environment, it loses w units of energy, so its energy changes to E2 = E1'-w = E1+q-w.

Though some of the heat is converted into work, that doesn't affect the fact that q units of heat were added, and w units of work are extracted. Thus the net energy change is q-w.

## 1. What is the 1st law of thermodynamics?

The 1st law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, but can only be transferred or converted from one form to another.

## 2. How does the 1st law of thermodynamics relate to energy?

The 1st law of thermodynamics states that energy is always conserved. This means that the total amount of energy in a closed system remains constant, even though it may change form. Energy can be converted from one form to another, such as from thermal energy to mechanical energy, but the total amount of energy remains the same.

## 3. Can the 1st law of thermodynamics be violated?

No, the 1st law of thermodynamics is a fundamental law of physics and has been extensively tested and proven. It is a universal law that applies to all energy interactions and cannot be violated.

## 4. How does the 1st law of thermodynamics apply to living organisms?

In living organisms, the 1st law of thermodynamics ensures that the energy flowing into an organism (through food, for example) is equal to the energy flowing out (through metabolism and other processes). This allows for the maintenance of energy balance and the ability to perform work and sustain life.

## 5. What is an example of the 1st law of thermodynamics in action?

An example of the 1st law of thermodynamics in action is a car engine. The chemical energy in the fuel is converted into heat energy, which then powers the engine and ultimately results in the movement of the car. The total energy in the system remains constant, but it is converted from one form to another to perform work.