1. Chemistry – Oct 12, 2016
P3 Challenge- (Try by memory before looking up)
1. Provide the elemental symbol for:
Copper, Sodium, Chlorine, Nitrogen, Hydrogen
2. Provide the elemental name for:
K, C, Ag, O, Ne
Objective –
Energy and Heat Capacity
Solutions and Solubility
Get out the Pressure-Temp WS for HMK check

2. Chemistry – Oct 12, 2016 Agenda – Assignment: - Energy Heat
Heat Capacity
Solutions
Solubility
Assignment: -
Heat and Solutions Worksheet

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. Endothermic process An endothermic process is one that absorbs energy.
You must heat an endothermic process to make it occur.
Energy is a reactant.
Surroundings gets colder.
E = Efinal – Einitial is positive
Energy E
Final state
Initial state

7. Exothermic process An exothermic process is one that releases energy.
The system will become colder.
Energy is a product.
Surroundings gets hotter. (explosion)
E = Efinal – Einitial is negative
Energy
Initial state
Final state E

8. Heat
Heat is the transfer of thermal energy either to or from a system.
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.

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
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
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.
Given a choice, use Joules form.
Note water’s extremely high value

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. 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.

12. Calorimetry 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?
How much aluminum can be heated from 5°C to 45°C by using 275 J of heat? (Specific heat capacity of Al = J/g°C)?
q =
m =
c =
ΔT =

13. Solubility Definitions
Solute, Solvent, Solution
Solubility – The number of grams of a substance that can be dissolved in 100 g of solvent (usually water) at a given temperature (usually 25◦C).
Saturated: A solution that contains the maximum amount of solute.
Can identify because there will be solid solute present.
Unsaturated: A solution that contains less than the maximum amount of solute possible.
Most solutions.
Supersaturated: A solution that contains more than the maximum amount of solute
A rare and unstable condition that is difficult to create.

14. Example
The solubility of KNO3 Potassium nitrate at 25 ◦C is 38.0 g in 100 g water.
If a solution contains 38.0 g in 100 g water at 25 ◦C, it is saturated.
If a solution contains less than 38.0 g in 100 g water at 25 ◦C, it is unsaturated.
If a solution contains more than 38.0 g in 100 g water at 25 ◦C, it is supersaturated.
A supersaturated example of sodium acetate in water. (Pretty Crystal)
How do you create a supersaturated solution?
Take a saturated solution, add extra solute, heat until all solute dissolves, then CAREFULLY and SLOWLY cool the solution back to the original temperature. The extra solid will stay in solution until a seed crystal is introduced, or the solution is agitated.

15. Solubility Curves
Plots the solubility at different temperatures for different substances.
Read solubility given temperature.
Read temperature for a given solubility.
Compare solubility of two temperatures.
For a solution described, determine saturated, unsaturated or supersaturated.
On line: Saturated, Below line: Unsaturated Above line: Supersaturated

16. Solubility Calculations
More or less than 100 g of water? Set up a proportion.
Ex: How many grams of substance A dissolve in 250 g of water at 30˚C.
The Solubility Curve tells you that 150 g of A dissolves in 100 g of water at 30˚C.
Then set up and solve this proportion:
𝟏𝟓𝟎 𝐠 𝑨 𝟏𝟎𝟎 𝐠 𝒘𝒂𝒕𝒆𝒓 = 𝒙 𝒈 𝑨 𝟐𝟓𝟎 𝐠 𝒘𝒂𝒕𝒆𝒓 Cross multiply to solve.
(100 g water)(x g A) = (150 g A)(250 g water)
x = 375 g A

17. Solubility of Gases
For solids, as temperature increases, solubility increases.
For gases, as temperature increases, solubility decreases.
Note that the solubility of a gas is MUCH lower than solids.
Milligrams in 1000 g water compared to grams in 100 g water
10,000 times smaller solubility
Solubility curve used the same way.

18. Exit Slip - Homework
Exit Slip: How much heat is needed to warm a 450 g copper pan from 25°C to 150°C ?
What’s Due? (Pending assignments to complete.)
Heat and Solutions Worksheet due Oct 17
What’s Next? (How to prepare for the next day)
Start reviewing for Test 2 Oct 19 – Look for Review Materials online