1 Chapter 2Energy and Matter 2.1 Energy

2 makes objects move, makes things stop. is needed to “do work.” Is part of all chemical processes – either liberated by the chemical change or else used to force the chemical change. Two forms – potential energy and kinetic energy Potential energy is a measure of the energy that could be liberated by a chemical or physical change (stored energy). Kinetic energy is a measure of the energy an object has by virtue of its movement. Energy

3 Work Work is done when you climb you lift a bag of groceries. you ride a bicycle. you breathe. your heart pumps blood. water goes over a dam. Copyright © 2009 by Pearson Education, Inc.

4 Potential Energy Potential energy is stored energy. Examples are water behind a dam. a compressed spring. chemical bonds in gasoline, coal, or food. Copyright © 2009 by Pearson Education, Inc.

5 Kinetic Energy Kinetic energy is the energy of motion. Examples are swimming. water flowing over a dam. working out. burning gasoline. Copyright © 2009 by Pearson Education, Inc.

6 Learning Check Identify the energy as potential or kinetic. A. Rollerblading B. a peanut butter and jelly sandwich C. mowing the lawn D. gasoline in the gas tank

7 Solution Identify the energy 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)

8 Heat is measured in joules or calories Joules (J) = 1 calorie (cal) calorie (cal) = 1 Joule (J) 1 kJ = 1000 J 1 kilocalorie (kcal) = 1000 calories (cal) 1 J = 1 kg m 2 sec -2 (energy is force acting through a distance) Units for Measuring Energy or Heat

9 Examples of Energy In Joules

10 Learning Check How many cal are obtained from a pat of butter if it provides 150 J of energy when metabolized? 1)0.36 cal 2)36 cal 3)630 cal

11 Solution How many cal are obtained from a pat of butter if it provides 150 J of energy when metabolized? Answer 2) Solution: Given: 150 J Need: calories Plan: J -> cal Equality: 1 cal = J Setup:150 J x 1 cal = 36 cal J