TEMPERATURE AND THERMAL ENERGY
Chapter 12.1
Kinetic Molecular Theory1. 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 1How 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 2A 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