Matthew Hursky, Brendan Donovan, Jacob Day, Vivian Zhang

*Heat and Thermodynamics

*Thermodynamics

*Thermodynamics: the study of heat and its transformation into mechanical energy

*Internal energy: amount of thermal energy within an object

*Heat flows between objects, thermal energy resides in objects, temperature is a measure of average kinetic energy

*Thermal Energy: Conduction

*Conduction: heat transfer through objects touching

*Atoms collide and transfer energy

*Heat is transferred until the objects are at thermal equilibrium (same temperature)

*Thermal Energy: Convection

*Convection: heat transfer through moving currents in gases/liquids

*Hot gases and hot liquids rise, creating convection currents

*Thermal Energy: Radiation

*Radiation: heat transfer through electromagnetic radiation

*No matter necessary

*Can occur in a vacuum

*First Law of Thermodynamics

heat added

increase in

internal energy

external work done

by the system

= +

*Processes

*Adiabatic process: when a gas is compressed or expanded so that no heat enters or leaves a system

*Isothermal process: when the temperature of the system remains constant

*Second Law of Thermodynamics

*Heat always flows from warmer objects to colder objects

*Heat Engines

*Heat engine: a device that changes internal energy (heat) into mechanical work

*Based on heat flowing from high temperature area (reservoir) to low temperature area (sink)

*Efficiency

*Ideal heat engine: converts internal energy completely into mechanical energy

*Carnot efficiency/ideal efficiency =

*Temperature measured in Kelvins

*Greater temperature difference greater efficiency

*Efficiency: Example

*If a steam engine has a heat reservoir temperature of 350 K and a sink temperature of 175 K, what is its ideal efficiency?

*ideal efficiency =

*Third Law of Thermodynamics

*No system can reach absolute zero

*Entropy

*Entropy: amount of disorder in a system

*Entropy tends to increase (2nd Law of Thermodynamics)

*Decreasing the entropy of a system requires work

*Multiple Choice #1

*The input heat in a heat engine is 600K(227 C) and the output is 300K(77 C). It’s ideal efficiency is:

*A) 25%

*B) 50%

*C) -50%

*D) 80%

*Multiple Choice #2

*How many calories are required to raise the temperature of 16 grams of water by 10 degrees C?

*A) 100 calories

*B) 120 calories

*C) 160 calories

*D) 200 calories

*Multiple Choice #3

*What is the rise in temperature when 20 calories are added to 10 grams of ice at -10 degrees C? Specific Heat of Ice: .5Cal/Grams X C

*A) 8 degrees C.

*B) 16 degrees C.

*C) 4 degrees C.

*D) 2 degrees C.

*Multiple Choice #4

*Ann is making pancakes. She burns her hand by touching the pan. What method of heat transfer explains this?

*A) Conduction

*B) Thermal Radiation

*C) Convection

*D) None of the above

*Multiple Choice #5

*How do you increase the internal energy of an object?

*A) Heat the system

*B) Do work on the system

*C) Both A & B

*D) None of the above

*Multiple Choice #6

*The First Law of Thermodynamics states that:

*A) when heat is added to a system, it will be lost

*B) when heat is added to a system, it will be transformed into twice as much energy

*C) when heat is added to a system, it will be transformed into an equal amount of energy

*D) adding heat is the only way to increase the internal energy of a system

*Multiple Choice #7

*Heat will flow:

*A) from cold to hot

*B) always upwards

*C) from hot to cold

*D) always downwards

*Multiple Choice #8

*The most efficient heat engine is one with:

*A) the smallest difference between input and output temperature

*B) a large difference between input and output temperature

*C) low input temperature and low output temperature

*D) high input temperature and high output temperature

*Multiple Choice #9

*The natural tendency of particles in a system is to:

*A) separate from different particles in the system

*B) continue moving in a straight line no matter what

*C) rapidly travel in small spirals

*D) create greater disorder

*Multiple Choice #10

*How is thermal energy transported from one place to another?

*I. Conduction

*II. Convection

*III. Radiation

A) I only

B) I and II only

C) II only

D) I, II and III

*Multiple Choice Key

1) B

2) C

3) C

4) A

5) C

6) C

7) C

8) B

9) D

10) D