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Chapter 2 Energy and Matter

2.1 Energy

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Energy

• 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

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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.

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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.

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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.

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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

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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)

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Heat is measured in joules or calories.

4.184 Joules (J) = 1 calorie (cal)

0.239 calorie (cal) = 1 Joule (J)

1 kJ = 1000 J

1 kilocalorie (kcal) = 1000 calories (cal)

1 J = 1 kg m2 sec-2

(energy is force acting through a distance)

Units for Measuring Energy or Heat

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Examples of Energy In Joules

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Learning Check

How many cal are obtained from a pat of butterif it provides 150 J of energy when metabolized?

1) 0.36 cal

2) 36 cal

3) 630 cal

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Solution

How many cal are obtained from a pat of butterif it provides 150 J of energy when metabolized?

Answer 2)Solution:Given: 150 JNeed: caloriesPlan: J -> calEquality: 1 cal = 4.184 JSetup: 150 J x 1 cal = 36 cal

4.184 J