Thermodynamics

Thermo – Heat

Dynamics – motion or flow

There are Three Laws of Thermodynamics that people have

figured out.

They seem to be true everywhere, but sometimes you have to adjust your

thinking to figure out the boundaries.

First Law

• Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred

In = Out

(Energy is conserved)

3 other ways of saying the 1st Law

• Energy can be neither created nor destroyed. It can only change forms.

• In any process in an isolated system, the total energy remains the same.

• For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system.

Second Law

• Heat never spontaneously flows from a cold substance to a hot substance.

Hot → Cold

(the only way you can make it go the other way is to add energy, which means it’s still true)

In other words • When two isolated systems in separate but nearby

regions of space, each in thermodynamic equilibrium in itself, but not in equilibrium with each other at first, are at some time allowed to interact, breaking the isolation that separates the two systems, and they exchange matter or energy, they will eventually reach a mutual thermodynamic equilibrium. The sum of the entropies of the initial, isolated systems is less than or equal to the entropy of the final exchanging systems. In the process of reaching a new thermodynamic equilibrium, entropy has increased, or at least has not decreased.

Third Law

• No system can reach Absolute Zero

0 K - -273.15 °C - -459.67 °F

C.P Snow’s Short Version

• 1 - You cannot win, you can only break even (that is, you cannot get something for nothing, because matter and energy are conserved).

• 2 - You cannot break even (you cannot return to the same energy state, because there is always an increase in disorder; entropy always increases).

• 3 - You cannot get out of the game (because absolute zero is unattainable).

Entropy

• Reduce the state of order of the initial systems, and therefore entropy is an expression of disorder or randomness

Maxwell’s Demon

DisclaimerAloha

I put together these power points for use in my science classes.You may use them in your classes.

Some images are public domain, some are used under the fair-use provisions of the copyright law, some are mine. Copyright is retained by the owners!

Ted Brattstrom