1

Heat Energy

“how we recognize that there were heat energy transferred between two

substances”

2

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

3

Learning Check

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

4

Learning Check

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

200 g400 g

5

Solution

2)14°C

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

200 g400 g

6

Some Equalities for Heat

Heat is measured in calories or joules

1 kcal = 1000 cal

1 calorie = 4.18J

1 kJ = 1000 J

7

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?

8

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.

9

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 0.39silver 0.057 0.24

gold 0.031 0.13

10

Learning Check

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

11

Solution

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

12

Measuring Heat

Requires

Temperature change T

Grams of substance

Specific heat of the substance

13

Bagaimana mengukur derajat panas sebuah benda?

We have to use Thermometer.

• Thermometers commonly have alcohol (with dye) or mercury

• Digital thermometers have replaced older ones

• Celsius is the metric scale for measuring temperature

• Water freezes at 0ºC and boils at 100ºC

What is the commonly scale for Thermometer?

14

• The Kelvin scale is a metric temperature scale measured in Kelvin units (K)

• Formula (273+ºC)= Kelvin

Kelvin scale

Question:• What is the boiling point of water on the Kelvin

scale? • What is the freezing point of water on the Kelvin

scale?

15

Absolute zero

Means that :

The temperature in which all molecular motion stops (0 K)

Question :

What is absolute zero on the Celsius scale?

16

Calculating Heat, Q

mass x temp. change x specific heat

m x T x c

17

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 = m x T x Sp. Ht. (H2O)

= 750 g x 28°C x 1.00 cal g°C

= 21 000 cal

18

Learning Check

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

19

Solution

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

20

Energy and Nutrition

1 Calorie (nutritional) = 1 kcal

1 Cal = 1000 cal

21

Caloric Food Values

Carbohydrate = 4 kcal/g

Fat = 9 kcal/g

Protein = 4 kcal/g

22

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 80chicken(no skin) 0 3 20 110

beef (3 oz) 0 5 22 130

23

Learning Check

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

24

Solution

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

25

Q = m L

• A phase change is a physical change that requires a change in heat energy

Example: the change of ice into water

• Energy needed to change the phase of the substance that is of mass m, is Q

Heat and Phase Changes

dengan L = kalor lebur (cal/gr)

Questions

What is freezing point, melting point, and boiling point?

What is a calorimeter?

• Device used to measure the heat given off during chemical reactions