Lecture5_2011.keyr

Lecture5_2011.keyr - Physical Properties of Water Hydrogen...

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Unformatted text preview: Physical Properties of Water Hydrogen bond Why is Earth so different or is it? Hydrological Cycle Boil at -70˚ C Freeze at -90˚ C By the way: 1 gallon = 4 quarts = 8 pints = 128 ounces = 231 cubic inches 1 liter = 0.2642 gallons = 1.0568 quart = 61.02 cubic inches 1 million gallons = 3.069 acre-feet = 133,685.64 cubic feet Planners estimate that one acre-foot serves the domestic needs of one to two families (five to eight people) 65,000 gallons per year per person; ~1,250 gallons per week Here's a quick rundown of some of water's properties: Weight: 62.416 pounds per cubic foot at 32 F ° Weight: 61.998 pounds per cubic foot at 100 F ° Weight: 8.33 pounds/gallon, 0.036 pounds/cubic inch Density: 1 gram per cubic centimeter (cc) at 39.2 F, 0.95865 gram per cc at 212 F True or False (1) Water contracts (gets smaller) when it freezes. (2) Water has a high surface tension. (3) Condensation is water coming out of the air. (4) More things can be dissolved in sulfuric acid than in water. (5) Rainwater is the purest form of water. (6) It takes more energy to heat water at room temperature to 212˚ F than it does to change 212˚ F water to steam. (7) If you evaporate an 8-inch glass full of water from the Great Salt Lake (with a salinity of about 20% by weight), you will end up with about 1 inch of salt. (8) Sea water is slightly more basic (the pH value is higher) than most natural fresh water. (9) Raindrops are tear-shaped. (10) Water boils quicker at Denver, Co. than at the beach. The earth appears to be unique in our solar system in that it contains an enormous amount of water, and that water has existed in a form not too different from its present state for billions of years (How do we know this?). Given that the laws of the nature operate everywhere in the solar system, we have to question why we are so privileged to have large bodies of liquid water on our planetary surface for so long a time. What makes the earth different from the other planets? 1) How did the earth acquire such a large amount of water in the first place, and 2) Once acquired, how was it retained ? • The formation of the earth probably took a few hundred million years to be completed. That is to be compared with the time of about 1 billion years since the earth has developed a solid crust. • About the time the earth was formed, the sun became large enough that the fusion reactions in the sun ignited. This didn't happen smoothly, but likely in sputtering way for a while. Each flaring up of the sun sent streams of particles sweeping out. If the earth had an atmosphere at this time, it would have been blown off leaving the earth as a rock with neither air or water on its surface. Solar energy is created deep within the core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F) and pressure (340 billion times Earth's air pressure at sea level) is so intense that nuclear reactions take place. This reaction causes four protons or hydrogen nuclei to fuse together to form one alpha particle or helium nucleus. • After the sun stabilized, the earth went through a process of releasing gases from its interior in a process called degassing. Over a relatively short time, something like a few 100 million years, enough material had been released to form the oceans and to give the earth an atmosphere. • There was no free oxygen in the atmosphere at this time, but it was a collection of gases, largely ammonia, methane and carbon dioxide, held to the earth by gravitational attraction. • Fortunately, early in its history, the temperature of the earth dropped below 212 degrees Fahrenheit, and the water condensed into the oceans we know today. • In fact, the mass of water present in the oceans, now about 10(24) grams, is about the same as the mass of water that was contained in the crust when the degassing process started. Estimate the rate at which water is being lost today by estimating the rate at which water molecules in the atmosphere are dissociated into its constituent hydrogen and oxygen. The hydrogen is light enough that it easily moves off into space. Hydrogen loss decreases the amount of water vapor in the atmosphere. ~ 5x10 (11) grams are lost this way each year. This amounts to a volume of a cube about 100 yards on a side. ~ 2x10(21) grams lost to space since the beginning of the earth thus amounts to about 0.2 percent of the water in the oceans. • This means that most of the water you see on the earth was the very same stuff that degassed from the crust when the earth was only a few hundred million years old. Fortunately, the water lost to space is replaced by the same geologic processes that formed the oceans originally. Atmospheric Evolution • primordial gases, later lost from sun's radiation 2. exhalations from the molten surface (volcanic venting); bombardment from icy comets 3. steady additions of carbon dioxide, water vapor, carbon monoxide, nitrogen, hydrogen, hydrogen chloride, ammonia, and methane from volcanic activity 4. addition of oxygen by plant/bacterial life "What makes the planets perfectly spherical?" Do earthquakes have effects on water sources? "What makes the planets perfectly spherical?" "If water properties (such as boiling point) changes at different elevations, how does elevation affect people in high elevations (considering we are made of mostly water)? Why is the water still here on the earth?, is more difficult to answer. • It has to do with the changing nature of the atmosphere due to evolution of life, specifically algae. The algae produced free oxygen by photosynthesis which destroyed ammonia and methane, so called greenhouse gases, just as the sun's luminosity was increasing by about twenty five percent. If that hadn't happened the oceans would have boiled away long ago. • In fact, we are the beneficiaries of an incredible balancing act which allowed just enough heat to escape from the earth to keep the oceans from boiling, but not so much as to cause the earth to freeze solid. Hydrologic Cycle - is responsible for the largest movement of a chemical substance on our planet. Water movement determines climatic patterns, plant growth, heat energy transfer, erosion rates, and rates of rock weathering • evaporation (latent heat input) about 500,000 km3 enough to cover the earth’s entire surface to a depth of about 1 m • transportation (water vapor and liquid - transports sensible heat) • precipitation (latent heat release) • infiltration (recharge groundwater) • transpiration (plants release into atmosphere) Atmospheric Circulation Cells also explain variations in precipitation with latitude: (Hadley, Ferrel) 0 degrees warm air rises, condenses- rain (low pressure) 30 degrees dry air descending and warms- deserts (high pressure) 60 degrees rain (low pressure) 90 degrees desert (high pressure) Then Add continents 1. physical barriers- deflect the winds 2. thermal effects 1. Effect of continentsLocation of high and low pressure systems varies with season as land heats and cools more than the sea • sea breezes • monsoons Southern hemisphere more zonal circulation due to less land Orographic effects- rain shadow Arid Region (desert) down stream of mountains If water’s heat capacity and latent heat of vaporization were much lower would we still have rain and would puddles of rainwater behave differently? ...
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