Specific heat capacity

When any substance absorbs heat, its temperature rises. The amount of heat that must be absorbed to produce a one-degree rise in temperature varies from one substance to another. It is known as the specific heat capac-

Specific heat capacity

ity of the substance, usually denoted by the symbol c, and is measured as the units of heat that must be absorbed for a one-degree increase in temperature. The scientific units are joules per gram per kelvin and are written as J g-1 K-1. Alternatively, the units can be given as calories per gram per degree Celsius (1°C = 1K), written as cal g-1 °C-1.

Specific heat capacity also varies slightly with temperature. When quoting values for c, therefore, it is necessary either to show them as a table, with values at a range of temperatures, or to specify the temperature to which the given value applies. The table below shows the specific heat capacities of several substances at specified temperatures, using both sets of units.

The table shows that water has the highest specific heat capacity of any common substance. One gram of fresh water at 59°F (15°C) must absorb 1 cal (4.19 J) of heat in order to raise its temperature by 1.8°F (1°C) and one gram of seawater at 62.6°F (17°C) must absorb 0.94 cal (3.93 J). This is almost twice as much heat as ice must absorb and approximately five times as much as most rocks must absorb. Consequently, the land, made from rock and sand, heats much faster than the sea during the day and during the summer. That is why, on a hot day, the sand may burn your feet as you run across it, but when you plunge into the lake or sea, the water feels cool. In winter the reverse happens, and the lake or sea remains warmer than the land for several months, because it takes a long time for the water to lose the warmth it absorbed in summer.

Water's capacity for absorbing a large amount of heat without raising its temperature is one of its most important properties, and it greatly affects climates. Air that passes across the ocean will be warmed by contact with it in winter and cooled in summer. Maritime climates, found in lands adjacent to the ocean, have a narrower temperature range than continental climates.

SPECIFIC HEAT CAPACITIES (c) OF COMMON SUBSTANCES

Substance

Temperature

c

°C

°F

J g-1 k-1

cal g-1 °C-1

freshwater

15

59

4.19

1.00

seawater

17

62.6

3.93

0.94

ice

-21--1

-5.8-30.2

2.0-2.1

0.48-0.50

dry air

20

68

1.006

0.2403

basalt

20-100

68-212

0.84-1.00

0.20-0.24

granite

20-100

68-212

0.80-0.84

0.19-0.20

white marble

18

64.4

0.88-0.92

0.21-0.22

quartz

0

32

0.73

0.17

sand

20-100

68-212

0.84

0.20

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