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Chapter 2 Energy and Matter

2.4 Specific Heat

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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

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Examples of Specific Heats

TABLE 2.6

cal/g°C0.2140.09200.03080.1080.05620.125

0.4880.5880.2070.100

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A. When ocean water cools, the surrounding air 1) cools. 2) warms. 3) stays the same.

B. 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.

Learning Check

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Heat Equation

Rearranging the specific heat expression gives theheat equation.

Heat = g x °C x J = J g°C

The amount of heat lost or gained by a substance iscalculated from the

• mass of substance (g).• temperature change (T).• specific heat of the substance (J/g°C).

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A. When ocean water cools, the surrounding air

2) warms.

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

at night. Sand must have a

2) low specific heat.

Solution

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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?

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Solution

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?

Given: 24.8 g metal, 275 J of energy, 20.2C to 24.5C Need: J/gC Plan: SH = Heat/gC

ΔT = 24.5C – 20.2C = 4.3 C

Set Up: 275 J = 2.6 J/gC (24.8 g)(4.3C)

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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

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Solution

How many kilojoules are needed to raise the temperature of 325 g of water from 15.5°C to 77.5°C?

3) 84.3 kJ

77.0°C – 15.0°C = 62.0°C

325 g x 62.0°C x 4.184 J x 1 kJ

g °C 1000 J

= 84.3 kJ