The Second Law of Thermodynamics The Hotter to

The Second Law of Thermodynamics The Hotter to the Cooler

The Second Law of Thermodynamics • In a closed system the following processes tend to occur spontaneously: – Energy tends to move until it is equally spread out throughout the system – Entropy (randomness) tends to increase • Closed system is one in which no objects or energy enters or leaves. • Spontaneous means there is no forcing by some outside mechanism • Statistical law that says what happens most of time NOT what always happens

Consequences of the Energy version of the 2 nd Law • Heat will flow from hot to cold • Things tend to seek position of lowest potential energy (think electrons in atoms and rolling down hill) • More and more easily useful energy is becoming less useful heat that will flow until entire universe is same temperature • Work becomes heat at 100% efficiency which will eventually result in a universe w/ the same temperature throughout and heat death.

The 2 nd Law Applied to a Heat Engine • No engine is 100% efficient • Ecarnot =Thot-Tcold /Thot x 100% – Efficiency increases with higher input tempertures – Efficiency increases with lower output temperatures – Later results in greater increases in efficiency • Work = Qout-Qin

The Entropy Version of the 2 nd Law • Entropy is the measurement of disorder • More disorder means more entropy • The second law says that entropy spontaneously increases w/ time – Gases tend to spread out – Matter tends to mix with other matter – Solids become liquids become gases – All energy will eventually become heat

Apparent Exceptions to the Second Law • Living things organize matter and energy in order to live – Produce heat in order to do this which increases entropy of universe and brings us that much closer to the end • A refrigerator pumps heat out of the inner compartment and dumps it into the hotter atmosphere – This is done by having a pump do work on a gas. This work will eventually become heat along with the heat dumped into the atmosphere and increase the entropy of the universe • Once in a great while things do become more ordered – Second law is a statistical law of probability that tells us what happens most of the time not what always happens