1. Chapter 16 Reaction Energy
West Valley High School
General Chemistry
Mr. Mata

2. Standard 7b
Students will know that chemical processes can either release or absorb thermal energy.

3. Essential Question:
How is heat used to measure energy in chemical reactions?

4. Heat vs Temperature Heat Temperature
measure of energy change in a system.
Temperature
measure of the kinetic energy (movement) of the particles in a system.
Gaining or losing heat energy in a substance can change its temperature.
Exothermic
System loses energy to surroundings.
Endothermic
System gains energy from surroundings.

5. Specific Heat Capacity
measure of how a substance reacts to heat energy changes.
The symbol we use is cp.
The “p” stands for pressure (constant) while heat is added or lost.
Specific Heat
property of matter, diff substances have diff specific heats.
heat energy required to raise 1 gram of pure substance 1 degree Celsius.

6. Specific Heat Capacity
Substance
J/g/oC or J/g/K
cal/g/oC or cal/g/K
Water (0 oC to 100 oC)
4.186
1.000
Zinc
.387
0.093
Ice (-10 oC to 0 oC)
2.093
0.500
Steam (100 oC)
2.009
0.480
Brass
.380
0.092
Wood (typical)
1.674
0.400
Soil (typical)
1.046
0.250
Air (50 oC)
Aluminum
.900
0.215
Tin
.227
0.205
Glass (typical)
.837
0.200
Iron/Steel
.452
0.108
Copper
0.0924
Silver
.236
0.0564
Mercury
.138
0.0330
Gold
.130
0.0310
Lead
.128
0.0305
Metals have very low cp,
why metals feel cold to touch.
Water has a very high cp,
4.184 J/g·0C
Substances with lower cp will rise in temperature faster and require less energy to do so than do substances with high cp.
1 calorie=4.184 Joules

7. Calculating Heat Energy
Cp=Joules / (gram * degree)
Change in heat (Joules, J) =
Change in temperature (degree, 0C) x
Mass (mass, g)
Specific Heat Capacity

8. Enthalpy, ΔH Enthalpy We specify enthalpy with ΔH. “Δ” means “change”.
heat energy transferred for a specific change to take place.
We specify enthalpy with ΔH.
“Δ” means “change”.
Exothermic reaction
negative enthalpy (-ΔH )
Endothermic reaction
Positive enthalpy (+ΔH).

9. Devices to Measure ΔHcomb
The Calorimeter (shown)
Heat energy transferred from a reaction inside the calorimeter to the water in the calorimeter. The temperature change of the water is observed.
A Bomb Calorimeter uses a chamber of pure oxygen to measure heats of combustion to the 1/1000 of a joule.

10. Reaction Enthalpy If ΔH is negative, reaction is exothermic.
C6H12O6 + 6O2 6CO2 + 6H kJ
ΔHrxn = kJ/mol
If ΔH is positive, reaction is endothermic.
2H2O kJ  2H2 + O2
ΔHrxn = kJ/mol
energy

11. Chapter 16 SUTW Prompt
Describe the differences between exothermic and endothermic in a chemical reaction.
Complete a sentence paragraph using the SUTW paragraph format. Hilight using green, yellow, and pink.
Due Date: Monday, March 12th, 2018 (start of class).