Properties of

Water

The first image taken by humans of the whole Earth. Photographed by the crew of Apollo 8, the photo shows the Earth at a distance of about 30,000 km. Space has no respect for “North” and “South” as the southern most tip of South America is at the top of the photo.

Boiling Point and Freezing Point

Substance Formula Mass, g

Melting Point, C

Boiling Point, C

Water, H2O 18.02 0 100

Ammonia, NH3 17.04 -77.7 -33.35

Methane, CH4 16.05 -182.5 -161.49

Methanol, CH3OH 32.04 -97.8 64.96

Ethanol, C2H5OH 46.08 -117.3 78.5

Sulfur dioxide, SO2 64.07 -72.7 -10

Carbon dioxide, CO2

44.01 -56.6@5.2 atm

-78.5sublimes

Source: CRC Handbook of Chemistry and Physics

Boiling Points for Water at Altitude

Altitude, ftBoiling point of

water, °C

0' (0m) 100°C

500' (152.4m) 99.5°C

1,000' (304.8m) 99°C

2,000' (609.6m) 98°C

5,000' (1524m) 95°C

6,000' (1828.8m) 94°C

8,000' (2438.4m) 91.9°C

10,000' (3048m) 89.8°C

12,000' (3657.6m) 87.6°C

14,000' (4267.2m) 85.5°C

Source: NOAA

Density

Water reaches a maximum density of 1.00 g/cm3 at a temperature of 3.98C.

Water expands (becomes less dense) as it freezes

Rock Weathering

The expansion of freezing water exerts sufficient force to fracture rock, and is a significant cause of rock weathering.

Water’s Thermochemistry

Specific heat and Latent heat of phase change, as they

apply to water.

Units for Measuring HeatThe Joule is the SI system unit for measuring heat:

The calorie is the heat required to raise the temperature of 1 gram of water by 1 Celsius degree

2

2111

s

mkgmeternewtonJoule

Joulescalorie 18.41

The British thermal unit (BTU or Btu) is the amount of energy needed to heat one pound of water by one degree Fahrenheit.

1 1055BTU Joules

Specific Heat

The amount of heat required to raise the temperature of one gram of substance by one degree Celsius.

1

2

3

45 6

7

8

9

1 10

2

3

45 6

7

8

9

11

Specific HeatThe amount of heat required to raise the temperature of one gram of substance by one degree Celsius.Substance Specific Heat (J/g·K)

Water (liquid) 4.18

Ethanol (liquid) 2.44

Water (solid) 2.06

Water (vapor) 1.87

Aluminum (solid) 0.897

Carbon (graphite,solid) 0.709

Iron (solid) 0.449

Copper (solid) 0.385

Mercury (liquid) 0.140

Lead (solid) 0.129

Gold (solid) 0.129

Specific Heat and Climate

How does water contribute to the moderation of climate in coastal communities?

SantaBarbar

aCA

Calculations Involving Specific Heat

cp = Specific Heat

Q = Heat lost or gained

T = Temperature change

OR

m = Mass

Tm

Qcp

pcTmQ

Energy and Phase Change

Along LEG ‘A’ water exists as a solid (ice), and the temperature increases as energy is absorbed.

The energy required to change the temperature of the ice is the specific heat of ice

Energy and Phase Change

At 0 C a phase change begins: Moving from left to right along LEG ‘B’, ice is melting to

form liquid water Moving from right to left along LEG ‘B’, liquid water is

freezing to form ice The distance of LEG ‘B’ along the Energy axis (x-axis) is

known as the Heat of FusionNote that temperature remains constant during a phase change!

Heat of Fusion

The energy that must be absorbed in order to convert solid to liquid at its melting point

The energy that must be removed in order to convert liquid to solid at its freezing point.

The heat of fusion of water is 334 Joules/gram

Energy and Phase Change

Once ice has completely melted, the temperature begins to increase again (LEG ‘C’), as the energy absorbed by water is no longer going toward changing the phase of the substance.

The energy required to change the temperature of the liquid water is its specific heat

Energy and Phase Change

At 100 C, a second phase change begins: Moving from left to right along LEG ‘D’, water is boiling to

form water vapor Moving from right to left along LEG ‘D’, water vapor is

undergoing condensation to form liquid water The distance of LEG ‘D’ along the Energy axis (x-axis) is

known as the Heat of VaporizationNote that temperature remains constant during a phase change!

Heat of Vaporization

The energy that must be absorbed in order to convert a liquid to gas at its boiling point.

The energy that must be removed in order to convert a gas to liquid at its condensation point.

The heat of vaporization of water is 2260 Joules/gram

Energy and Phase Change

Once all of the liquid water has vaporized, the temperature begins to increase again (LEG ‘E’), as the energy absorbed by water is no longer going toward changing the phase of the substance.

The energy required to change the temperature of the steam is its specific heat

Latent Heat – Sample Problem

Problem: The heat of fusion of water is 334 J/g.How much energy is needed to convert60 grams of ice at 0C to liquid water at 0C?

Massof ice Heat

offusion

2

2

60 33420040 20.04

1

g H O JJoules kilojoules

g H O

Latent Heat – Sample Problem

Problem: The molar heat of fusion of water is6.009 kJ/mol. How much energy is needed to convert60 grams of ice at 0C to liquid water at 0C?

Massof ice

MolarMass ofwater

Heatof

fusion

2 2

2 2

60 1 6.00920.04

18.02 1

g H O mol H O kJkiloJoules

g H O mol H O