Laws of Thermodynamics

ZEROTH LAW OF THERMODYNAMICSIf two thermodynamic systems (bodies) are

separately in thermal equilibrium with a third, they are also in thermal equilibrium with each other.

Thermal equilibrium means no heat transfer between bodies.

A C BC

A B

FIRST LAW OF THERMODYNAMICSPrinciple of Conservation of Energy:

Energy can be changed from one form to another, but it cannot be created or destroyed.

The total amount of energy and matter in the universe remains constant, merely changing from one form to another.

FIRST LAW OF THERMODYNAMICS

Q = W + ΔUHeat added to system = Work Done by system

+ change in Internal Energy of systemEnergy put in equals work done plus

change in internal energy of gas.Work and heat are due to processes which

add or subtract energy, ΔU is not.

A TIP ON HOW TO KEEP THE 1ST LAW STRAIGHT IN YOUR MIND

ΔU = Q + (- W)Use algebra to isolate the change in Internal EnergyNow think of the system as your bodyWhen heat is added to a system, its internal energy

is increased…think of your body when you drink a hot beverage—your internal energy goes up

When you do work (-W), your internal energy is reduced

Example ProblemWhat is the energy change in a system if 330

J of heat are absorbed by the system and 310 J of work are done on the system?

∆U = Q + (-W)

∆U = (330J) + (+310J)

∆U = 640 J

Work done to system is +

Heat added to system is +

Example ProblemWhat is the energy change in a system if 330

J of heat are absorbed by the system and 310 J of work are done on the system?

∆U = Q+(-W)

∆U = (330J) + (+310J)

∆U = 640 J

Work done to system is +

Heat added to system is +

SECOND LAW OF THERMODYNAMICSLaw of Increased Entropy

Entropy (symbolized by S), is a measure of the disorder of a system (random ways in which a system behaves).

“In all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state.“

The total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value.

SECOND LAW OF THERMODYNAMICS

A system's energy is the sum of its useful energy and its useless energy

Entropy may be visualized as the "scrap" or "useless" energy.

Entropy is directly proportional to the absolute temperature of the considered system.

SECOND LAW OF THERMODYNAMICSIn a system, a process that occurs will tend

to increase the total entropy of the universe.Clausius statement: Heat generally cannot

spontaneously flow from a material at lower temperature to a material at higher temperature.

Kelvin statement: It is impossible to convert heat completely into work.

SECOND LAW OF THERMODYNAMICS

Ice melting - a classic example of an increase in entropy

By Anton at de.wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], from Wikimedia Commons

THIRD LAW OF THERMODYNAMICSAbsolute Zero

Determines an absolute reference point for the determination of entropy.

As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.Example: water