Water and the Fitness of the Environment

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Heat and Temperature

Kinetic energy is the energy of motion

Heat is a measure of the total amount of kinetic energy due to molecular motion

Temperature measures the intensity of heat due to the average kinetic energy of molecules

Slide 13

The Celsius scale is a measure of temperature using Celsius degrees (°C)

A calorie (cal) is the amount of heat required to raise the temperature of 1 g of water by 1°C

The “calories” on food packages are actually kilocalories (kcal), where 1 kcal = 1,000 cal

The joule (J) is another unit of energy where 1 J = 0.239 cal, or 1 cal = 4.184 J

Slide 14

Water’s High Specific Heat

The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC

The specific heat of water is 1 cal/g/ºC

Water resists changing its temperature because of its high specific heat

Slide 15

Water’s high specific heat can be traced to hydrogen bonding

Heat is absorbed when hydrogen bonds break

Heat is released when hydrogen bonds form

The high specific heat of water minimizes temperature fluctuations to within limits that permit life

Slide 16

Fig. 3-5

San Diego 72°

40 miles

Pacific Ocean

70s (°F)

80s

90s

100s

Santa Barbara 73°

Los Angeles

(Airport) 75°

Burbank

90°

San Bernardino

100°

Riverside 96°

Santa Ana

84°

Palm Springs

106°

Slide 17

Evaporative Cooling

Evaporation is transformation of a substance from liquid to gas

Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to gas

As a liquid evaporates, its remaining surface cools, a process called evaporative cooling

Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water

Slide 18

Insulation of Bodies of Water by Floating Ice

Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense

Water reaches its greatest density at 4°C

If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth

Slide 19

Fig. 3-6

Hydrogen

bond

Liquid water

Hydrogen bonds break and re-form