Chapter 2 Energy and Matter

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Energy

• makes objects move.

• makes things stop.

• is needed to “do work”.

Energy

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 © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Potential Energy

Potential energy isenergy stored for use ata later time.

Examples are

• water behind a dam.

• a compressed spring.

• chemical bonds in gasoline, coal, or food. Copyright © 2005 by Pearson Education, Inc.

Publishing as Benjamin Cummings

Kinetic Energy

Kinetic energy is the

energy of matter in motion.

Examples are

• swimming.

• water flowing over a dam.

• working out.

• burning gasoline.Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Learning Check

Identify the energy as potential or kinetic.

A. roller blading

B. a peanut butter and jelly sandwich

C. mowing the lawn

D. gasoline in the gas tank

Heat is measured in joules or calories.

4.184 Joules (J) = 1 calorie (cal) (exact)

1 kJ = 1000 J

1 kilocalorie (kcal) = 1000 calories (cal)

Units for Measuring Energy or Heat

Examples of Energy In Joules

Learning Check

How many calories are obtained from a pat of butter

if it provides 150 J of energy when metabolized?

Calorimeters

A calorimeter

is used to measure heat transfer.

• can be made with a coffee cup and a thermometer.

• indicates the heat lost by a sample

• indicates the heat gained by water.

Energy and Nutrition

On food labels, energy is shown as the nutritional

Calorie, written with a capital C. In countries other

than the U.S., energy is shown in kilojoules (kJ).

1 Cal = 1000 calories

1 Cal = 1 kcal

1 Cal = 1000 cal

1 Cal = 4184 J

1 Cal = 4.184 kJ

Caloric Food Values

The caloric or energy values for foods indicate the

number of kcal(Cal) provided by 1 g of each type of food.

Carbohydrate: 4 kcal

1 g

Fat (lipid): 9 kcal

1 g

Protein: 4 kcal

1 g

Energy Values for Some Foods

TABLE 2.2

Energy Requirements

• The amount of energy needed each day depends on age, sex, and physical activity.

TABLE 2.3

A cup of whole milk contains 12 g of carbohydrate, 9.0 g of fat, and 5.0 g of protein. How many kcal (Cal) does a cup of milk contain?

1) 48 kcal (or Cal)

2) 81 kcal (or Cal)

3) 150 kcal (or Cal)

Learning Check

Temperature

Temperature

• is a measure of how hot or cold an object is compared to another object.

• indicates that heat flows from the object with a higher temperature to the object with a lower temperature.

• is measured using a thermometer.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Temperature Scales

Temperature Scales

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

• are Fahrenheit, Celsius, and Kelvin.

• have reference points for the boiling and freezing points of water.

A. What is the temperature of freezing water?

1) 0°F 2) 0°C 3) 0 K

B. What is the temperature of boiling water?

1) 100°F 2) 32°F 3) 373 K

C. How many Celsius units are between the boiling and freezing points of water?

1) 100 2) 180 3) 273

Learning Check

Celsius Formula

1.8

32-F C

Solving A Temperature Problem

A person with hypothermia has abody temperature of 94.6°F. What is that temperature in °C?

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

A pepperoni pizza is baked at 455°F. What temperature is needed on the Celsius scale?

1) 423°C

2) 235°C

3) 221°C

Learning Check

The Kelvin temperature scale

• is obtained by adding 273 to the Celsius temperature.

TK = TC + 273

• contains the lowest possible temperature, absolute zero (0 K).

0 K = –273°C

Kelvin Temperature Scale

Temperatures

TABLE 2.5

What is normal body temperature of 37°C in Kelvins?

1) 236 K

2) 310. K

3) 342 K

Learning Check

Specific heat

• is different for different substances.

• is the amount of heat that raises the temperature of 1 g of a substance by 1°C.

• in the SI system has units of J/gC.

• in the metric system has units of cal/gC.

Specific Heat

Examples of Specific Heats

TABLE 2.6

cal/g°C0.2140.09200.03080.1080.05620.125

0.4880.5880.2070.100

Heat Equation

q = m x C x T

• m: mass of substance

• C: specific heat of the substance T: temperature change

Learning Check

What is the specific heat of a metal if 24.8 g absorbs275 J of energy and the temperature rises from 20.2C to24.5C?

How many kilojoules are needed to raise the temperature of 325 g of water from 15.0°C to 77.0°C?

1) 20.4 kJ

2) 77.7 kJ

3) 84.3 kJ

Learning Check