Important Terms & Notes

Conceptual PhysicsMar. 12, 2014

Chapter 24 Review QuestionsQuestions 1 - 8

1. Greek meaning: Movement of Heat2. Thermodynamics is concerned with

Macroscopic processes. 3. Lowest possible temperatures:

a. On Kelvin scale : 0° K b. On Celsius Scale: -273° C

4. Temperature of Melting Ice on the Absolute Scale: +273 ° K

Chapter 24 Review QuestionsQuestions 1 -8 (cont.)

4. Temperature of Boiling Water on the Absolute Scale: +373 ° K

5. Energy cannot be created nor destroyed; therefore , Energy (Heat) added to a system can only change to an equal amount of another form of energy.

ΔQ = ΔE +W

Chapter 24 Review QuestionsQuestions 1 -8 (cont.)

6. Work done on a system should result in an increase of the Internal Energy of that System. The temperature of that system should increase as well since the average kinetic energy of the system has increased.

7. ΔQ = ΔEi + W

8. Work done on a system should result in an increase in the Internal Energy of that System. Work done by a system should result in an decrease in the Internal Energy of that System.

Thermodynamics Class Problem Set #1 - 1

• In a given system 50J of heat is added to the system but NO work is done by the system. What is the system’s increase in Internal Energy?

ΔQ = ΔEi + W

ΔEi = ΔQ - W ΔQ = 50J W=0

ΔEi = ΔQ - W = 50J - 0 = 50J

Thermodynamics Class Problem Set1- 2

• If 125J of thermal energy is added to a system, how much work can be performed if the internal energy increases by 37J?

ΔQ = ΔEi + W W = ΔQ - ΔEi

ΔQ = 125J, ΔEi = 37J

W = 125J – 37J =88J

Thermodynamics Class Problem Set1 - 3

• A given system has performed 735J of work. Its internal Energy increased by 235J. How much energy was added to this system?

ΔQ = ΔEi + W

ΔE = 235J, W = 735J

ΔQ = 235J + 735J = 970J

First Law of Thermodynamics

• Heat added to a system is transformed into an equal amount of some other form of energy.

• A version of the Law of Energy Conversion

ΔQ = ΔEi + W

Adiabatic

• The term applied to the expansion or compression of a gas occurring without the gain or loss of heat.

• Example: Automobile Engine

Second Law of Thermodynamics

• Heat will never of itself flow from one object to another of higher temperature.

• Heat will not flow from Cold to Hot without work being performed.

The Refrigeration Cycle

Energy Interchange in a Refrigerator’s Cooling Cycle

• Heat is taken in from the inner compartment as the Refrigerant (liquid) evaporates in the pipes (Evaporator) and changes phase to vapor.

• The vapor is compressed and then pumped through a heat exchanger pipe assembly (Condenser) where heat is given up to the outside environment allowing the vapor to condense into liquid.

Heat Engine

A Device that Changes Internal Energy into Mechanical Energy

Carnot Efficiency

• The Ideal maximum percentage of input energy that can be converted into work in a heat engine.

• Ideal Efficiency = (Thot – Tcold)/Thot

Entropy

• A measure of the amount of disorder in a system.

ΔS = Δ Q/T