properties of water the first image taken by humans of the whole earth. photographed by the crew of...
TRANSCRIPT
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 [email protected] 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