Laws of Thermodynamics:
Zeroth, 1st, 2nd Laws

What is the Zeroth law?

First off - this law is called ``Zeroth'' because its felt to be so fundamental that it gets the ÔzeroÕ declaration. In fact, they thought of this law way after the first three and because of its purported import, it was made the Zeroth, not the fourth law.

Secondly, the law is pretty ÔobviousÕ, but then again the more obvious something is the more profound it ends up being because it is the ground work for the definition of temperature.

OK the definition: The Zeroth law states that two systems (A and B) are in thermal equilibrium when (1) both systems are at equilibrium, (2) when A meets B they remain in equilibrium. Also, this law states that if another system (C) exists, and A is in equilibrium with B, and B is in equilibrium with C, then A is in equilibrium with C. Pretty intuitive. Don't spend too much time on it, just read it, understand it and move on.

What is the 1st Law of Thermodynamics?

Also known as the Law of Conservation of Energy:

Law 3   In a closed universe where only System A and B exist, the total energy that enters into A equals the total energy that leaves System B.

Another way of looking at it: the internal energy of System A can only change if it absorbs or transfers energy by heat and/or work to another System B. The change in internal energy will be of the same magnitude but different signs for the Systems A and B.

Although beyond the scope of the MCAT - but an interesting footnote - Albert Einstein's discovery of special relativity reflects the Law of Conservation of Energy, showing that mass and energy are interchangeable: $E=mc^{2}$.

In quantum mechanics, conservation of energy is not true because of HeisenbergÕs uncertainty principle.

How is the change in internal energy calculated?

$$\Delta E = Q - W$$ (38.3)

Where $\Delta E$ is the change of energy in the system, $Q$ is heat transferred into the system from the surroundings, and $W$ is work done by the system.

What are mechanical, electrical, thermal and chemical energy units?

Table 37.4: Mechanical, electrical, thermal and chemical energy units

		$Conversion$
Mechanical	$Joule$	1 J
Electrical	$eV$	1eV = $1.60 \times 10^{-19}$ J
Thermal	$cal*$	1 cal = 4.1855 J
Chemical	$kJ$	1 kJ = 1000 J
	$kcal**$	1 kcal = 1000 cal = 4,185 J

* One calorie is the amount of heat necessary to raise the temperature of 1 g of water from 14.5 $^{o}$C to 15.5 $^{o}$C; it is equal to 4.1855 $J$. The nutritional calorie represents 1000 of these 15 $^{o}$C calories.

** 1 kcal

What is the 2nd Law of Thermodynamics?

A mathematically complex law that explains entropy and how energy moves about us:

The 2nd law of thermodynamics, briefly, states that energy will flow from more Òconcentrated areasÓ to less concentrated areas.

A good example is a pot of boiling water on the stove. Take the pot off, and the pot/water will transfer their energy into the cooler kitchen air.