1. Physics 2 – Feb 9, 2017
P3 Challenge – How much heat from the sun is required to increase the temperature of 15.3 kg of aluminum siding from 20C to 48C? (The specific heat capacity for aluminum = 900 J/kgK.)
Today’s Objective:
3.1 Thermal Physics; Calorimetry
Assignment:
Ch 3.1, p125, #7-12
Get out # 1-6 for a HMK check
Agenda
Homework Review
Phase changes
Heating graph for water
Heat for phase changes
Calorimetry

2. Phase Changes
There are six phase changes you should be aware of. 4 are very common, 2 are rare and are not in the IB book.
Solid  Liquid = melting (at m.p)
Liquid  Solid = freezing (at m.p)
Liquid  Gas = evaporation (at any temp) or boiling (at b.p)
Gas  Liquid = condensation (at b.p)
(Solid  Gas = sublimation)
(Gas  Solid = deposition)

3. Heating Curve This is the heating curve for water.
The first slope is the q = mcT for ice up to 0C.
At 0C it melts at constant T.
The second slope is the q = mcT for water up to 100C.
At 100C, it boils at constant T.
The third slope is the q = mcT for steam from 100C up.

4. Heat during Phase changes
For the constant temperature phase changes, Q = mL
Where L is the specific latent heat of fusion for melting and freezing and
Where L is the specific latent heat of vaporization for boiling and condensation.
The unit for L is J/kg or kJ/kg or J/g
Note the similarity between this equation and Q= mcT.

5. Calorimetry (method of mixtures)
water
Calorimetry is the measurement of heat.
In general, with any kind of calorimetry, there is some hot substance giving off heat and something else picking up that heat.
The amount of heat lost by the hot object = amount of heat gained by the cold object.
Or to say it another way, the energy of the total system is conserved.

6. Calorimetry problem
A 525 g lead ball at a temperature of 100.0C is placed in a 25.0 g aluminum calorimeter containing g of water at 17.5°C. Find the equilibrium temperature of the system.
Final temperature = 19.7°C

7. Exit Slip - Assignment
Exit Slip- 235 J of heat is added to a 16.5 g sample of iron initially at 23.0C. What is the final temperature of the sample? (c = 450 J/kg K)
What’s Due on Feb 10? (Pending assignments to complete.)
Ch 3.1, p125, #7-12
What’s Next? (How to prepare for the next day)
Read 3.1 p about Thermal Energy