# 1st and 2nd laws of thermodynamics

• fabius53

#### fabius53

While refreshing some thermodynamics for a personal interest in renewable energies, I drafted a reasoning that apparently leads from the 1st law to the 2nd law of thermodynamics, so that the latter, at least for ideal gases undergoing reversible processess, would seem to be just a consequence of the former.
Shortly, the reasoning starts from 1st law and ideal gas law, through Mayer's relation, the dependence of internal energy on just temperature, a general expression of the heat exchange $$\delta$$Q, adiabatic slope, Carnot's theorem and finally 2nd law; in detail, it is included here (1stlaw-2ndlaw.pdf).
As far as I remember, 1st law and 2nd law of thermodynamics are basic laws (at least without involving statistical thermodynamics), so I tend to think that there must be some flaw in my reasoning.
Can anyone help me spot any flaws ? Or is the reasoning correct only under very restrictive hypotheses ? Can anyone maybe help me understand more deeply thermodynamics laws ?
I appreciate any contribution

#### Attachments

• 1stlaw-2ndlaw.pdf
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You use relations for ideal gases that were derived assuming the second law of thermodynamics in one way or another. It is not surprising that you can extract it again from these relations.

## What is the first law of thermodynamics?

The first 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.

## What is the second law of thermodynamics?

The second law of thermodynamics states that the total entropy of a closed system always increases over time. Entropy is a measure of the disorder or randomness in a system.

## How do the first and second laws of thermodynamics relate to each other?

The first law of thermodynamics is a statement of energy conservation, while the second law is a statement of the direction of energy flow. Together, they explain how energy behaves in a closed system.

## 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 mechanical energy to power the car's movement. The total amount of energy remains constant, but it is converted from one form to another.

## What are some real-world implications of the second law of thermodynamics?

The second law of thermodynamics has several real-world implications, such as the fact that energy cannot be 100% efficient and that all natural processes tend towards disorder. It also helps explain why perpetual motion machines are impossible and why energy sources are limited.