1. Chemistry – Oct 22, 2018
P3 Challenge – Distinguish between a triple point and a critical point.
Turn in States Phet Activity if not yet
Turn in PT Units HMK if not yet

2. Chemistry – Oct 22, 2018 Objective – Agenda – Assignments
Energy and Heat Capacity
Solutions and Solubility
Assignments
Heat Worksheet
Agenda –
Energy
Heat
Heat Capacity
Heating Curve of Water (time permitting)

3. What is Energy? Energy = Ability to do work
Law of Conservation of Energy: Energy is neither created nor destroyed.
It can only be transformed from one form to another or transferred from one system to another.
Total energy of a system = Kinetic Energy + Potential Energy
Kinetic energy – Energy of motion
Potential energy – Stored energy

4. Kinetic Energy Types Thermal energy – Energy of random motion of atoms
Electromagnetic energy – Energy of light
Sound energy – Energy of motion of atoms due to pressure differences
Electrical energy – Energy of the flow of electrons

5. Potential Energy Types
Gravitational potential energy – Energy of position within Earth’s gravity
Electrical potential energy – Energy of separation of electric charge (voltage)
Chemical potential energy – Energy contained within chemical bonds
Nuclear potential energy – Energy contained within the nucleus

6. Heat
Heat is the transfer of thermal energy either to or from a system.
Heat is given the symbol, Q.
Positive heat transfers heat to a system. (Endothermic process)
Temperature of substance increases
Negative heat releases heat to the surroundings. (Exothermic process)
Temperature of substance decreases
Each substance absorbs/releases at a characteristic rate called it’s heat capacity. A substance with a high heat capacity requires a large amount of energy to change its temperature.

7. Endothermic process Energy E Final state Initial state
An endothermic process is one that absorbs heat.
You must heat an endothermic process to make it occur.
Energy is a reactant.
Q, heat is positive
The system gets hotter.
Surroundings gets colder.
T = Tfinal – Tinitial is positive Tf > Ti
Energy E
Final state
Initial state

8. Exothermic process Energy Initial state Final state E
An exothermic process is one that releases heat.
An explosion is an exothermic process (easy way to remember)
Energy is a product.
Q, heat is negative
The system gets colder.
Surroundings gets hotter.
T = Tfinal – Tinitial is negative Tf < Ti
Energy
Initial state
Final state E

9. Specific heat capacity, c
Substance
c in J/g K
c in cal/g ◦C
Aluminum
0.900
0.215
Bismuth
0.123
0.0294
Copper
0.386
0.0923
Brass
0.380
0.092
Gold
0.126
0.0301
Iron
0.460
0.101
Lead
0.128
0.0305
Silver
0.233
0.0558
Tungsten
0.134
0.0321
Zinc
0.387
0.0925
Mercury
0.140
0.033
Alcohol(ethyl)
2.4
0.58
Water
4.186
1.00
Ice (-10 C)
2.05
0.49
Granite
.790
0.19
Glass
.84
0.20
Specific heat capacity, c
If the heat capacity is per gram of material, it is the specific heat capacity, c.
Specific heat capacity is the amount of energy needed to raise the temperature of 1 gram of substance by 1 degree Celsius. Typical units are cal/g◦C or J/gK.
◦C and K are interchangeable for these units.
Problems may use either Joules or calories.
Given a choice, use Joules form.
Note water’s extremely high value
1 Food Calorie = 1 kcal (note the capital C)

10. Measuring heat, q
For any change in temperature from Tinitial to Tfinal, ΔT = Tfinal – Tinitial
For a temperature increase, ΔT is positive.
For a temperature decrease, ΔT is negative.
Heat exchanged during the temperature change is given by:
Where q is the heat, m is the mass of the substance, c is the specific heat capacity of the substance and ΔT is the temperature change.

11. Heat calculations q = m = c = ΔT =
Ex: How much heat is needed to raise 2.50 g of water from 25 ◦C to body temperature of 37 ◦C?
What mass of aluminum can be heated from 5°C to 45°C by using 275 J of heat? (Specific heat capacity of Al = J/g°C)?
What is the final temperature when 36.4 J of of heat is lost from a 23.8 g piece of lead initially at 85°C? (Specific heat capacity of Pb = J/g°C)?
q =
m =
c =
ΔT =

12. Heating Curve of Water Heat and temperature are not the same.
Phase changes occur at a constant temperature, but still require heat to happen.
Not all phase changes require the same amount of heat
It takes more energy to boil than to melt.
It takes more heat to warm water than ice or steam the same amount.
The slopes of the ice and steam lines are greater than the line for water.

13. Exit Slip - Homework
Exit Slip: How much heat is needed to warm a 450 g copper pan from 25°C to 150°C ? (Use joules)
What’s Due? (Pending assignments to complete.)
Heat Worksheet
What’s Next? (How to prepare for the next day)
Start reviewing for Test 2 Oct 31