# Question about thermodynamics first law

• Clara Chung
In summary, the equation dU = TdS - PdV is a physical property relationship that must be satisfied for any material. It describes the relationship between changes in internal energy, entropy, and volume between two closely neighboring thermodynamic equilibrium states. This equation is not specific to any process, reversible or irreversible, as it is based on state functions.

#### Clara Chung

I know that dS=dQ/T for reversible process,
is dU=TdS-PdV for reversible process only?

Clara Chung said:
I know that dS=dQ/T for reversible process,
is dU=TdS-PdV for reversible process only?
This equation has nothing to do with any process. It is a physical property relationship that must be satisfied for any material, describing the relationship between the mutual changes in U, S, and V between and two closely neighboring thermodynamic equilibrium states of the material. This constraint is imposed as a consequence of the 2nd law of thermodynamics.

Clara Chung
Agree with Chestermiller, dU = TdS-pdV is nothing to do with the process, (reversible or irreversible), even though it is developed from the reversible process, since all of the qualities here are state functions. Therefore, they are just related to the state.

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

The first law of thermodynamics is the principle of conservation of energy, stating that energy cannot be created or destroyed, only transferred or converted from one form to another.

## 2. How does the first law of thermodynamics relate to heat and work?

The first law of thermodynamics states that the total energy of a closed system remains constant. This means that any heat added to a system must either be converted into work or increase the internal energy of the system.

## 3. Can the first law of thermodynamics be violated?

No, the first law of thermodynamics is a fundamental law of nature and cannot be violated. It has been extensively tested and proven to hold true in all physical and chemical processes.

## 4. What is an example of the first law of thermodynamics in action?

An example of the first law of thermodynamics is a car engine, where the chemical energy from the fuel is converted into heat, which is then converted into mechanical energy to move the car.

## 5. How does the first law of thermodynamics affect energy efficiency?

The first law of thermodynamics sets a limit on the maximum efficiency of any energy conversion process. This means that it is impossible to convert 100% of the energy input into useful work, as some energy will always be lost in the form of heat.