what is the difference between 1st and 2nd law of thermodynamics?

Answer 1

The first law of thermodynamics deals with the conservation of energy. The second law deals with entropy and the like.

Answer 2

Paraphrased, the first law says that the change in energy of a given system equals heat in, minus heat out. More precisely:

"The increase in the internal energy of a thermodynamic system is equal to the amount of heat energy added to the system minus the work done by the system on the surroundings."

So, it's like a bank account: if you have $100 at the start of the day, add $50 and lose $25 in bounced check fees, you have $125.

The second law of thermodynamics says that entropy increases. Specifically: "The entropy of an isolated system not at equilibrium will tend to increase over time, approaching a maximum value." In practical terms, it means that heat flows from hot things to cold things, not the other way 'round. Overall, the second law means one day everything will be the same temperature, and it will be impossible for anything to change- maximum entropy, everything at the same temperature.

As Allen Ginsberg would have it:
* First law of thermodynamics - "You can't win."
* Second law of thermodynamics - "You can't break even."
* Third law of thermodynamics - "You can't quit." (Because you can never get to absolute zero.)

See also the references, as below.

Answer 3

The First Law of Thermodynamics says that "energy cannot be created nor destroyed; it can only change forms".

The Second Law of Thermodynamics essentially defines the direction in which energy can move.

Using the first law of thermodynamics only, one can argue that a cup of coffee (hot) can be made hotter by taking energy from the surrounding air (room temperature). This doesn't occur naturally but instead the coffee loses heat to the surrounding air and is made cooler.
Both situations (the coffee heating up and the coffee cooling down) are legal as far as the first law goes (as long as energy is conserved) but it is the second law which makes it possible only for the coffee to cool down.

A simple statement of the second law ... absent outside influences, a process changes towards equilibrium to reach equilbrium. Hot coffee cools down to reach room temperature, it doesn't heat up to reach it...

E-Mail me, [e-mail], if you have any other questions. I have a BSME so I should be able to help you out.

Answer 4

First law basically says: Change in internal energy = heat added to the system - work done by the system --------------------------------------... Second law pertains to inefficiencies in the heat engine : The Carnot cycle is a great example of the second law. The carnot predicts the maximum level of efficiency you can obtain from a heat engine based on heat temperature inputs - heat temp output - the work obtained from that temperature differential. It is impossible to extract an amount of heat Qh from a hot reservoir and use it all to do work W . Some amount of heat Qc must be exhausted to a cold reservoir. This precludes a perfect heat engine. So this law says you cannot get more work from a heat engine than you put into it in work plus heat together

Answer 5

First law explains conservation of energy. Second law states that work requires exchange of energy from outside the system. The second law explains why perpetual motion machines cannot work. Machines cannot use its own energy to work, another source (reservoir) is needed to refuel the machine.

Answer 6

1st law: energy can neither be created nor destroyed.

2nd law: Heat travels spontaneously from a hotter body to a cloder body.

These are the basic definitions, but the difference is clearly shown here.