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 18.02 100 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 -78.5 sublimes Source: CRC Handbook of Chemistry and Physics
Boiling Points for Water at Altitude Altitude, ft Boiling 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 Heat The 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 The British thermal unit (BTU or Btu) is the amount of energy needed to heat one pound of water by one degree Fahrenheit.
Specific Heat The amount of heat required to raise the temperature of one gram of substance by one degree Celsius.
Specific Heat The 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)
Specific Heat and Climate Santa Barbara CA How does water contribute to the moderation of climate in coastal communities?
Climate Comparison Visalia, CA Jan Feb Mar Apr May Jun Average high in °F: 55 61 67 73 82 89 Average low in °F: 39 42 46 49 56 62 Av. precipitation in inch: 1.93 1.85 2.01 0.94 0.35 0.16 Santa Barbara, CA Jan Feb Mar Apr May Jun Average high in °F: 65 66 69 70 71 Average low in °F: 46 48 50 52 55 58 Av. precipitation in inch: 4.37 4.57 2.91 1.22 0.31 0.08 Source: USClimateData.com
Climate Comparison Visalia, CA Jul Aug Sep Oct Nov Dec Average high in °F: 94 93 88 78 64 55 Average low in °F: 67 65 60 53 44 38 Av. precipitation in inch: 0.16 0.59 1.22 1.73 Santa Barbara, CA Jul Aug Sep Oct Nov Dec Average high in °F: 75 76 73 69 65 Average low in °F: 60 56 50 47 Av. precipitation in inch: 0.04 0.16 0.91 1.77 3.03 Source: USClimateData.com
Calculations Involving Specific Heat OR cp = Specific Heat Q = Heat lost or gained T = Temperature change m = Mass
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 Fusion Note 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 Vaporization Note 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 convert 60 grams of ice at 0C to liquid water at 0C? Mass of ice Heat of fusion
Latent Heat – Sample Problem Problem: The molar heat of fusion of water is 6.009 kJ/mol. How much energy is needed to convert 60 grams of ice at 0C to liquid water at 0C? Mass of ice Molar Mass of water Heat of fusion