1. 3.4 Energy Energy makes objects move. makes things stop.
is defined as the ability to do work.
A defibrillator provides electrical
energy to heart muscle to re-establish normal rhythm.
Learning Goal Identify energy as potential or kinetic; convert between units of energy.

2. Kinetic Energy
Kinetic energy is the energy of motion. Examples are the following:
swimming
water flowing over a dam
working out
The movement of water that flows from the top of a dam is an example of kinetic energy.

3. Potential Energy
Potential energy is energy stored for use at a later time.
Examples are the following:
water at the top of a dam
a compressed spring
chemical bonds in gasoline, coal, or food
The water at the top of a dam has potential energy by virtue of its position. As the water falls over and down the dam, the potential energy is converted to kinetic energy.

4. Study Check
Identify the energy in each example as potential or kinetic: A. rollerblading B. a peanut butter and jelly sandwich C. mowing the lawn D. gasoline in the gas tank

5. Solution
Identify the energy in each example as potential or kinetic: A. rollerblading kinetic B. a peanut butter and jelly sandwich potential C. mowing the lawn kinetic D. gasoline in the gas tank potential

6. Heat and Energy
Heat is the energy associated with the movement of particles.
The faster the particles move, the greater the heat or thermal energy of the substance.
Given an ice cube, as heat is added, the H2O molecules
that are moving slowly increase their motion.
eventually have enough energy to change the ice cube from a solid to a liquid.
Core Chemistry Skill Using Energy Units

7. Units of Energy Energy is measured in
the SI unit, the joule (J), or in kilojoules (kJ), 1000 joules.
units of calories (cal) or in kilocalories (kcal), 1000 calories.
The calorie is defined as the amount of energy needed to raise the temperature of 1 g of water by 1 °C.

8. Energy Comparison

9. Study Check
How many calories are obtained from a pat of butter if it provides 150 J of energy when metabolized? A cal B. 630 cal C. 36 cal

10. Solution
How many calories are obtained from a pat of butter if it provides 150 J of energy when metabolized? STEP 1 State given and needed quantities. STEP 2 Write a plan to convert the given unit to the needed unit. joules calories
ANALYZE Given Need
THE PROBLEM J calories
Energy
Factor

11. Solution
How many calories are obtained from a pat of butter if it provides 150 J of energy when metabolized? STEP 3 State the equalities and conversion factors.

12. Solution
How many calories are obtained from a pat of butter if it provides 150 J of energy when metabolized? STEP 4 Set up the problem to calculate the needed quantity. Answer is C. ×