1. Law of Conservation of Energy
“Energy can neither be created nor destroyed.”
The total amount of energy in the universe is constant. There is no process that can increase or decrease that amount.
However, we can transfer energy from one place in the universe to another, and we can change its form.
Tro's "Introductory Chemistry", Chapter 3

2. Matter Possesses Energy
When a piece of matter possesses energy, it can give some or all of it to another object.
It can do work on the other object.
All chemical and physical changes result in the matter changing energy.
Tro's "Introductory Chemistry", Chapter 3

3. Kinds of Energy Kinetic and Potential
Potential energy is energy that is stored.
Water flows because gravity pulls it downstream.
However, the dam won’t allow it to move, so it has to store that energy.
Kinetic energy is energy of motion, or energy that is being transferred from one object to another.
When the water flows over the dam, some of its potential energy is converted to kinetic energy of motion.
Tro's "Introductory Chemistry", Chapter 3

4. Tro's "Introductory Chemistry", Chapter 3
Some Forms of Energy
Electrical
Kinetic energy associated with the flow of electrical charge.
Heat or Thermal Energy
Kinetic energy associated with molecular motion.
Light or Radiant Energy
Kinetic energy associated with energy transitions in an atom.
Nuclear
Potential energy in the nucleus of atoms.
Chemical
Potential energy in the attachment of atoms or because of their position.
Tro's "Introductory Chemistry", Chapter 3

5. Tro's "Introductory Chemistry", Chapter 3
Units of Energy
Calorie (cal) is the amount of energy needed to raise one gram of water by 1 °C.
kcal = energy needed to raise 1000 g of water 1 °C.
food calories = kcals.
Energy Conversion Factors
1 calorie (cal) =
4.184 joules (J)
1 Calorie (Cal)
1000 calories (cal)
1 kilowatt-hour (kWh)
3.60 x 106 joules (J)
Tro's "Introductory Chemistry", Chapter 3

6. Tro's "Introductory Chemistry", Chapter 3
Energy Use
Unit
Energy Required to Raise Temperature of 1 g of Water by 1°C
Energy Required to Light 100-W Bulb for 1 Hour
Energy Used by Average U.S. Citizen in 1 Day
joule (J)
4.18
3.6 x 105
9.0 x 108
calorie (cal)
1.00
8.60 x 104
2.2 x 108
Calorie (Cal)
1.00 x 10-3
86.0
2.2 x 105
kWh
1.1 x 10-6
0.100
2.50 x 102
Tro's "Introductory Chemistry", Chapter 3

7. Tro's "Introductory Chemistry", Chapter 3
Exothermic Processes
When a change results in the release of energy it is called an exothermic process.
An exothermic chemical reaction occurs when the reactants have more chemical potential energy than the products.
The excess energy is released into the surrounding materials, adding energy to them.
Often the surrounding materials get hotter from the energy released by the reaction.
Tro's "Introductory Chemistry", Chapter 3

8. An Exothermic Reaction
Surroundings
reaction
Potential energy
Reactants
Products
Amount of energy released
Tro's "Introductory Chemistry", Chapter 3

9. Endothermic Processes
When a change requires the absorption of energy it is called an endothermic process.
An endothermic chemical reaction occurs when the products have more chemical potential energy than the reactants.
The required energy is absorbed from the surrounding materials, taking energy from them.
Often the surrounding materials get colder due to the energy being removed by the reaction.
Tro's "Introductory Chemistry", Chapter 3

10. An Endothermic Reaction
Surroundings
reaction
Potential energy
Products
Reactants
Amount of energy absorbed
Tro's "Introductory Chemistry", Chapter 3

11. Tro's "Introductory Chemistry", Chapter 3
Temperature Scales
Fahrenheit scale, °F.
Used in the U.S.
Celsius scale, °C.
Used in all other countries.
A Celsius degree is 1.8 times larger than a Fahrenheit degree.
Kelvin scale, K.
Absolute scale.
Tro's "Introductory Chemistry", Chapter 3

12. Temperature Scales Celsius Kelvin Fahrenheit Rankine 100°C 373 K 212°F
Boiling point water
298 K
75°F
534 R
Room temp
25°C
0°C
273 K
32°F
459 R
Melting point ice
-38.9°C
234.1 K
-38°F
421 R
Boiling point mercury
-183°C
90 K
-297°F
162 R
Boiling point oxygen
BP helium
-269°C
4 K
-452°F
7 R
-273°C
0 K
-459 °F
0 R
Absolute
zero
Celsius
Kelvin
Fahrenheit
Rankine

13. Tro's "Introductory Chemistry", Chapter 3
Temperature Scales
The Fahrenheit temperature scale used as its two reference points the freezing point of concentrated saltwater (0 °F) and average body temperature (96 °F).
More accurate measure now sets average body temperature at 98.6 °F.
Room temperature is about 72 °F.
Tro's "Introductory Chemistry", Chapter 3

14. Temperature Scales, Continued
The Celsius temperature scale used as its two reference points the freezing point of distilled water (0 °C) and boiling point of distilled water (100 °C).
More reproducible standards.
Most commonly used in science.
Room temperature is about 22 °C.
Tro's "Introductory Chemistry", Chapter 3

15. Tro's "Introductory Chemistry", Chapter 3
Fahrenheit vs. Celsius
A Celsius degree is 1.8 times larger than a Fahrenheit degree.
The standard used for 0° on the Fahrenheit scale is a lower temperature than the standard used for 0° on the Celsius scale.
Tro's "Introductory Chemistry", Chapter 3

16. The Kelvin Temperature Scale
Both the Celsius and Fahrenheit scales have negative numbers.
Yet, real physical things are always positive amounts!
The Kelvin scale is an absolute scale, meaning it measures the actual temperature of an object.
0 K is called absolute zero. It is too cold for matter to exist because all molecular motion would stop.
0 K = -273 °C = -459 °F.
Tro's "Introductory Chemistry", Chapter 3

17. Tro's "Introductory Chemistry", Chapter 3
Kelvin vs. Celsius
The size of a “degree” on the Kelvin scale is the same as on the Celsius scale.
The 0 standard on the Kelvin scale is a much lower temperature than on the Celsius scale.
When converting between kelvins and °C, remember that the kelvin temperature is always the larger number and always positive!
Tro's "Introductory Chemistry", Chapter 3

18. Energy and the Temperature of Matter
The amount the temperature of an object increases depends on the amount of heat energy added (q).
If you double the added heat energy the temperature will increase twice as much.
The amount the temperature of an object increases depending on its mass.
If you double the mass, it will take twice as much heat energy to raise the temperature the same amount.
Tro's "Introductory Chemistry", Chapter 3