TEMPERATURE AND THERMAL ENERGY

Chapter 12.1

Kinetic Molecular Theory

1. Everything is made of particles

2. These particles move

3. Hot things move faster than cold things

Definitions

Temperature – a measure of average kinetic energy of an object

Thermometer - device that measures temperature (and, as a result, average KE)

Heat Flow

Always from hot to cold objects

Heat flow stops only when all objects are in equilibrium (at the same temp)

Example 1

If A is 75 degrees and B is 25 degrees, at which temperature are they both in equilibrium? To solve, first add up the different

temperatures Next, divide the total temp by 2 (because we

have 2 objects) This is the equilibrium temperature

Answer = 50 degrees

Absolute zero

The temp at which molecular motion stops

Is this cold or hot??

Temperature conversion

Know how to do these…

50°C = _______ K

325 K = ________°C

Temp scales

Conduction

Energy transfer when objects are in direct contact. There must be matter in order for energy to transfer by conduction.

Convection

Energy transfer by air or water currents. Objects are not in direct contact Look for currents Know that hot air and water rises!! Matter is required for heat transfer by

convection

Radiation

Energy transfer thru empty space No matter is required!! Its how the sun heats the Earth Sunbathers are often used as examples of

heating by radiation

Examples

Example 2

Example 3

Heat Transfer Formula

Q = CmΔTQ = heat gained or lost (J)m = mass in kgC = specific heat (see p.279)ΔT = temp change (K or °C)

Solving for a final temp when 2 objects are mixed or in contact

Tf = maCaTai + mbCbTbi

maCa + mbCb

Example Problem 1

How much heat is needed to raise the temperature 1.5 kg of water from 22°C to 35°C?

m = 1.5 kgΔT = 15°CC = ?? What is changing temperature? Use

the specific heat for whatever is changing temp

(see page 279)

Q = 4180 x 1.5 x 15Q = 94,050 J

Example Problem 2

A 5.0 kg sample of water at 25°C is mixed with 1.5 kg of water at 75°C. What is the final temperature of the mixture?

Use the Tf formula…

Tf = 5 x 4180 x 25 + 1.5 x 4180 x 755 x 4180 + 1.5 x 4180

Tf = 459800 + 47025020900 + 6270

Tf = 34°C

Work

Page 296 #’s 23 – 24 and 27-28

Phase Change Diagram