1. Chapter 16: Energy and Chemical Change
Table of Contents
Chapter 16: Energy and
Chemical Change
16.1: Energy
16.2: Heat in Chemical Reactions and Processes
16.3: Thermochemistry
16.3: Thermochemical Equations
16.4: Calculating Enthalpy Change

2. universe = system + surroundings
Energy and Chemical Change: Basic Concepts
Chemical Energy and the Universe
universe = system + surroundings
The Universe is everything around us
the System: the specific part of the universe that you are studying.
the Surroundings: everything else

3. Energy is the ability to do work or produce heat.
Energy and Chemical Change: Basic Concepts
The Nature of Energy
Energy is the ability to do work or produce heat.
Potential energy: stored energy.
Kinetic energy: the energy of movement.

4. Chemical potential energy: stored in bonds
Energy and Chemical Change: Basic Concepts
The Nature of Energy
Chemical potential energy:
stored in bonds
The energy stored in a substance because of its composition :
the type of atoms in the substance
the number and type of chemical bonds joining the atoms
the way atoms are arranged.

5. Molecular kinetic energy: Measure of molecular “speed”
Energy and Chemical Change: Basic Concepts
The Nature of Energy
Molecular kinetic energy: Measure of molecular “speed”
Measured by a thermometer: As temperature increases, the motion of submicroscopic particles increases. So a thermometer is like a molecular speedometer.

6. Chemical systems contain both kinetic energy and potential energy.
Energy and Chemical Change: Basic Concepts
The Nature of Energy
Chemical systems contain both kinetic energy and potential energy.
Law of conservation of energy: energy can be converted from one form to another, but it is neither created nor destroyed.
suppose you have money in two accounts at a bank and you transfer funds from one account to the other. Although the amount of money in each account has changed, the total amount of your money in the bank remains the same.
the first law of thermodynamics

7. Chemical potential energy
Energy and Chemical Change: Basic Concepts
Chemical potential energy
Heat (symbol=q), is the flow of kinetic energy due to temperature changes.
Exothermic = gives off heat (hot)
Forming bonds – releases energy
Endothermic = takes in heat (cold)
Breaking bonds – requires energy
Heat always travels from hot to cold.

8. 1,000 calories = 1 kilocal = 1 Calorie
Energy and Chemical Change: Basic Concepts
Measuring heat
UNITS
calorie (cal): metric unit of energy
the amount of energy required to raise the 1 gram of water 1° Celsius
1,000 calories = 1 kilocal = 1 Calorie
dietary Calories
chemistry calories

9. joule (J): The SI unit of heat and energy
Energy and Chemical Change: Basic Concepts
Measuring heat
UNITS
joule (J): The SI unit of heat and energy
4.184 joules = 1 calorie
1,000 J = 1 kJ
(Calories are bigger than joules)

10. Converting Energy Units Steps for converting units:
Energy and Chemical Change: Basic Concepts
Converting Energy Units
Steps for converting units:
1. Find your goal
2. Start with what you know
3. Use conversion factors to change units
4. Check that units cancel

11. Converting Energy Units
Ex1) How much energy in joules is 270 nutritional Calories?
Goal = Joules Known = 270 Calories
J = 270 Cal
1000 cal
4.184 J
= J
1,129,680
1 Cal
1 cal
= 1.1 x 106 J
convert Cal to cal
convert cal to J
How much is that? Combustion of 1 mol methane is the less than the energy that you get from this clif bar. It’s WOW!

12. Practice converting energy units
Ex2) Convert 142 Nutritional Calories into calories.
Ex3) An exothermal reaction releases 86.5 kJ. How many kilocalories of energy are released?
Ex 4) If an endothermic process absorbs 256 J, how many kilocalories are absorbed?
142,000 cal
20.7 kcal
kcal

13. used to determine the specific heat of unknown metals
Energy and Chemical Change: Basic Concepts
Measuring Heat
Calorimeter: a device used to measure the amount of heat absorbed or released during a chemical or physical process.
used to determine the specific heat of unknown metals

14. Each substance has its own specific heat.
Energy and Chemical Change: Basic Concepts
Specific Heat
The specific heat (c): the amount of heat required to raise the temperature of 1 gram of any substance by 1° C.
Each substance has its own specific heat.
Why? Because different substances have different compositions.
specific heat (c) of water = J/(g∙°C)

15. ∆T = |Tfinal – Tinitial|
Energy and Chemical Change: Basic Concepts
Calculating heat evolved and absorbed
Heat absorbed or released by a substance during a change in temperature:
specific heat
(J/g ·°C)
mass (g)
Change in temperature (°C)
HEAT (J)
∆T = |Tfinal – Tinitial|

16. Calculating Specific Heat
Energy and Chemical Change: Basic Concepts
Calculating Specific Heat
Ex5) The temperature of a sample of iron with a mass of 10.0 g changed from 50.4°C to 25.0°C with the release of 114 J heat. What is the specific heat of iron? q
114 J
c = = =
m · ΔT
(10.0 g)
|25.0°C-50.4°C|
114 J = =
.449 J/(g·°C)
(10.0 g)
(25.4°C)

17. Using Data from Calorimetry
Energy and Chemical Change: Basic Concepts
Using Data from Calorimetry
Ex6) A piece of metal with a mass of 4.68 g absorbs 256 J of heat when its temperature increases by 182°C. What is the specific heat of the metal?
Known
Unknown
mass of metal = 4.68 g metal
specific heat
c = ? J/(g·°C)
heat absorbed, q = 256 J
∆T = 182°C
c = .301 J/(g·°C)

18. Practice specific heat equation
Ex7) If the temperature of 34.4 g of ethanol increases from 25.0°C to 78.8°C, how much heat has been absorbed?
Ex 8) 4.50 g of gold [c = J/(g·°C)] absorbed J of heat. If the initial temperature was 25.0°C, what was the final temperature?
4.52 x 103 J
5.00 x 102 °C

19. End day 1