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Chapter 6Energy and States of Matter

Measuring Heat Energy

Energy and Nutrition

LecturePLUS Timberlake 99

Heat

- Energy that flows from something warm to something cooler
- A hotter substance gives KE to a cooler one
- When heat is transferred (lost or gained), there is a change in the energy within the substance

LecturePLUS Timberlake 99

Learning Check H1

A. When you touch ice, heat is transferred

from

1) your hand to the ice

2) the ice to your hand

B. When you drink a hot cup of coffee, heat

is transferred from

1) your mouth to the coffee

2) the coffee to your mouth

LecturePLUS Timberlake 99

Solution H1

A. When you touch ice, heat is transferred

from

1) your hand to the ice

B. When you drink a hot cup of coffee, heat

is transferred from

2) the coffee to your mouth

LecturePLUS Timberlake 99

Learning Check H2

When you heat 200 g of water for 1 minute, the water temperature rises from 10°C to 18°C.

If you heat 400 g of water at 10°C in the same pan with the same amount of heat for 1 minute, what would you expect the final temperature to be?

1) 10 °C 2) 14°C 3) 18°C

400 g

200 g

LecturePLUS Timberlake 99

Solution H2

2)14°C

Heating twice the mass of water using the same amount of heat will raise the temperature only half as much.

400 g

200 g

LecturePLUS Timberlake 99

Some Equalities for Heat

Heat is measured in calories or joules

- 1 kcal = 1000 cal
- 1 calorie = 4.18J
- 1 kJ = 1000 J

LecturePLUS Timberlake 99

Specific Heat

- Why do some foods stay hot longer than others?
- Why is the beach sand hot, but the water is cool on the same hot day?

LecturePLUS Timberlake 99

Specific Heat

Different substances have different capacities for storing energy

It may take 20 minutes to heat water to 75°C. However, the same mass of aluminum might require 5 minutes and the same amount of copper may take only 2 minutes to reach the same temperature.

LecturePLUS Timberlake 99

Specific Heat Values

Specific heat is the amount of heat needed to raise the temperature of 1 g of a substance by 1°C

cal/g°C J/g°C

water 1.00 4.18

aluminum 0.22 0.90

copper 0.093 0.39

silver 0.057 0.24

gold 0.031 0.13

LecturePLUS Timberlake 99

Learning Check H3

A. A substance with a large specific heat

1) heats up quickly 2) heats up slowly

B. When ocean water cools, the surrounding air

1) cools 2) warms 3) stays the same

C. Sand in the desert is hot in the day, and cool

at night. Sand must have a

1) high specific heat 2) low specific heat

LecturePLUS Timberlake 99

Solution H3

A. A substance with a large specific heat

2) heats up slowly

B. When ocean water cools, the surrounding air

2) warms

C. Sand in the desert is hot in the day, and cool

at night. Sand must have a

2) low specific heat

LecturePLUS Timberlake 99

Measuring Heat

Requires

- Grams of substance
- Temperature change T
- Specific heat of the substance

LecturePLUS Timberlake 99

Heat Calculations

A hot-water bottle contains 750 g of water at 65°C. If the water cools to body temperature (37°C), how many calories of heat could be transferred to sore muscles?

heat = g x T x Sp. Ht. (H2O)

750 g x 28°C x 1.00 cal g°C

= 21 000

LecturePLUS Timberlake 99

Learning Check H4

How many kcal are needed to raise the temperature of 120 g of water from 15°C to 75°C?

1) 1.8 kcal

2) 7.2 kcal

3) 9.0 kcal

LecturePLUS Timberlake 99

Solution H4

How many kcal are needed to raise the temperature of 120 g of water from 15°C to 75°C?

2) 7.2 kcal

120 g x (75°C - 15°C) x 1.00 cal x 1 kcal

g°C 1000 cal

LecturePLUS Timberlake 99

Foods and Calories

Food Carbo Fat Protein Energy(kcal

carrots,

1 cup 11 0 1 50

banana 26 0 1 110

egg 0 6 6 80

chicken

(no skin) 0 3 20 110

beef (3 oz) 0 5 22 130

LecturePLUS Timberlake 99

Learning Check H5

1.0 cup of whole milk contains 12 g of carbohydrate, 9.0 g of fat, and 9.0 g of protein. How many kcal (Cal) are obtained?

1) 48 kcal

2) 81 kcal

3) 165 kcal

LecturePLUS Timberlake 99

Solution H5

3) 165 kcal

12 g carbo x 4 kcal/g = 48 kcal

9.0 g fat x 9 kcal/g = 81 kcal

9.0 g protein x 4 kcal/g = 36 kcal

Total kcal = 165 kcal

LecturePLUS Timberlake 99

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