Chapter 12

The Laws of Thermodynamics

Work in a Gas Cylinder

PV Diagrams

First Law of Thermodynamics What is first law of

thermodynamics? What does it do? What is the equation? How do I use it?

First Law – Signs Signs of the terms in the equation

Q Positive if energy is transferred to the system by

heat Negative if energy is transferred out of the

system by heat W

Positive if work is done on the system Negative if work is done by the system

U Positive if the temperature increases Negative if the temperature decreases

Molar Specific Heat

Degrees of Freedom

Isolated System

Second Law of Thermodynamics What is the second law? What does it do? How do I use it?

Types of Thermal Processes Isobaric

Pressure stays constant Horizontal line on the PV diagram

Isovolumetric Volume stays constant Vertical line on the PV diagram

Isothermal Temperature stays the same

Adiabatic No heat is exchanged with the surroundings

Cyclic Processes

Heat Engine

Thermal Efficiency of a Heat Engine

Heat Pumps and Refrigerators

Reversible and Irreversible Processes

Sadi Carnot 1796 – 1832 French Engineer Founder of the

science of thermodynamics

First to recognize the relationship between work and heat

Carnot Cycle

Example

How much work is done by an ideal gas in expanding isothermally from an initial volume of 3 liters at 20 atm to a final volume of 24 liters?

ExampleYou have one and half hour before guest start arriving to your party when you suddenly realized that you forgot to buy ice for your drinks. You quickly put 1.0 L of water at 10 degree Celsius into your ice cube tray and pop them into the freezer. Will you have ice for your guest. The label on your refrigerator states that COP=5.5 and power rating 550W. Assume that only 10% of power contributes to freezing water.

Example

Find the efficiency of an Otto cycle shown in the figure and express the answer in terms of the ratio R=Va/Vb.

Entropy What is entropy?