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.

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.

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.

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

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

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

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.

Energy Comparison

Study Check How many calories are obtained from a pat of butter if it provides 150 J of energy when metabolized? A. 0.86 cal B. 630 cal C. 36 cal

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 150 J calories Energy Factor

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.

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. ×