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Ch. 1: Water Section 1: The Nature of Water

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Presentation on theme: "Ch. 1: Water Section 1: The Nature of Water"— Presentation transcript:

1 Ch. 1: Water Section 1: The Nature of Water
Section 2: Why is Water Necessary? Section 3: Recycling Water

2 Water About 70% of the human body is water
It fills and surrounds cells Helps to move nutrients throughout the body, control body temperature, eliminate wastes, digest foods, and lubricate joints Oceans, lakes, rivers and streams are habitats for many organisms

3 Water Exists in three states (phases) on Earth: solid, liquid, gas
One molecule is made up of two hydrogen atoms and one oxygen atom. Chemical formula: H2O

4 Changing Forms of Water
Water molecules are held together by weak, covalent bonds. A covalent bond forms when elements join by sharing electrons

5 Changing Form When water changes state, thermal energy is either absorbed by the water or given off to the environment. In order to do this, the covalent bonds have to be broken or reformed

6 Changing Forms of Water
To reach high energy states, heat energy must be used to break bonds joining the atoms Breaking bonds requires heat energy, which is absorbed by the water molecule When lowering energy states, water releases heat energy back into the environment

7 Recap High Energy States Low Energy States Solid  Liquid  Gas
Water molecule absorbs heat Greater heat = molecules moving faster = greater kinetic energy = higher energy state Low Energy States Gas  Liquid  Solid Water molecule releases heat Less heat = molecules moving slower = less kinetic energy = lower energy state

8 Changing Forms of Water
No matter the direction of the state or phase change, the amount of energy required for the change will always be equal.

9 Energy States The following energy states cool the environment because the water is absorbing heat energy to break the bonds Melting (solid  liquid) Vaporization (liquid  gas) Sublimation (solid  gas)

10 Energy States The following energy states heat the environment because the water is releasing heat energy while it reforms the broken bonds Freezing (liquid  solid) Condensation (gas  liquid) Deposition (Sublimation) (gas  solid)


12 Latent Heat of Fusion The amount of heat needed to melt ice
It takes about 355 joules of heat to melt 1 gram of ice. AND/OR the amount of heat released by water as it freezes About 355 joules of heat are released to the environment when 1 gram of water freezes. Both occur at 0oC

13 Latent Heat of Vaporization
The amount of heat needed to make water evaporate It takes about 2,260 joules of heat to make 1 gram of water turn to water vapor. AND/OR the amount of heat released by water vapor when it condenses back into water About 2,260 joules of heat energy are released back into the environment when 1 gram of water vapor condenses into liquid water.

14 Changing States It takes a while for phase changes to occur. While the phase change is taking place, no change in temperature occurs. All the energy is going toward making the water change states. The temperature starts to rise again once all of the water has changed states.


16 Density The amount of mass in a unit of volume
Density of pure water: 1.0 g/cm3

17 You can change the density of water two ways
Add another substance to it, such as salt, and it becomes more dense Ex: Where rivers flow into the ocean, the less dense freshwater will float on top of the denser seawater until waves and currents mix them together. Increase its temperature and it becomes less dense Ex: Water is colder at the bottom of the ocean than at the top. This difference can lead to density currents.

18 A Polar Molecule Is a molecule that has a slightly positive end and a slightly negative end because electrons are shared unequally. Water is a polar molecule because the O atom pulls harder on the electrons than the two H atoms do. This makes the O atom slightly negative and the H atoms slightly positive.


20 Cohesion Since water molecules are polar they act like tiny magnets, which causes an attraction between water molecules. This results in a number of properties that are unique to water molecules only!

21 Because of Cohesion… Water forms into drops.
Water remains liquid at room temperature. The attraction between molecules prevents evaporation Surface Tension – cohesive forces on the surfaces of water allows molecules to share bonds with their neighbors Allows insects/reptiles to run across water


23 Capillary action – ability of water to be drawn through narrow tubes due to adhesion.
Helps water to rise against gravity inside plants Adhesion – attraction of water to other molecules.

24 Some other effects of bonding…
Water is the universal solvent! It is great for dissolving other substances such as sea salts and other substances that travel through your body. Ice floats on liquid water. When water freezes, the weak bonds between the molecules form an open arrangement of molecules

25 Specific Heat The amount of energy that is needed to raise the temp. of 1kg of substance 1oC. Water has a high specific heat = takes a while to heat up or cool down. Helps plants and animals to regulate their body temperatures. Helps keep us cool when its hot. Prevents tissues from freezing when cold.

26 Section 2 Why is Water Necessary?

27 Reasons Societies Use Water
Production Transportation Recreation

28 Production Used in processing and cooling during manufacturing
Used in mining and refining processes Agriculture uses 41% of all water in the U.S. Most of this water is used for irrigation.

29 Transportation Passenger liners Ferries
Big ships are often the most economical way to move large freight long distances.

30 Recreation Fishing Swimming SCUBA diving Boating Etc.

31 Valuable Resource Water is a valuable resource that must be conserved and protected. It is not only important for use in homes and society, but it is also important for maintaining ecological balance in nature. Pollutants such as oil, chemicals, radioactive material, and litter harm wildlife.

32 Conserving Water Less than 1% of all water on Earth is available for all uses except transportation. Certain practices can help to conserve water.

33 Agriculture Irrigation - most water is lost due to evaporation. Rather than flood fields, farmers can use sprinklers, drip tubing, or computer sensors to signal when crops need water. Mulching also helps to conserve water by slowing down evaporation rates.

34 Industry Industries can treat and reuse the same water over and over.

35 What can you do? About half of all water used in the U.S. is wasted due to evaporation, leaks, etc. Turn water off when soaping up, brushing teeth, etc. Install low-flow toilets and shower heads Use ornamental plants that don’t require a large amount of water

36 Section 3 Recycling Water

37 Did you know? Water has been around for billions of years. The water you drink may have been in Galileo’s tea cup or drank by a dinosaur! Water on Earth is constantly being recycled through a process known as the water cycle. (See fig. 17)

38 Why is it Important to Conserve Water?
Although 70% of Earth’s surface is covered in water, 97% is salt water. Of the only approximately 3% that is fresh water, 3/4 of that is locked up in the form of ice as glaciers. Of the less than 1% that is useful to us, much lies below ground.

39 Oceans “Water, water everywhere, but not a drop to drink.”
Cannot use to drink, bathe, or irrigate Removing salt (called desalination) usually isn’t practical

40 Ice 77% of Earth’s fresh water is locked up as ice
Glaciers are common near the poles Ex: Greenland and Antarctica have many glaciers

41 Groundwater Not all rain makes its way into rivers and lakes as runoff, some infiltrates into the ground. Groundwater is water that is held underground in layers of rock and sediment. Soil Water - water that is held in openings in the soil

42 Surface Water Includes lakes, rivers, ponds, etc. Water is easily used

43 Water in the Atmosphere
Air holds water, too (0% - 4% water by volume). Warm air can hold more water than cold air. Clouds need water vapor to form. Source of rain, sleet, snow (collectively referred to as precipitation)

44 Heats atmosphere when condenses to form clouds
Cools atmosphere when evaporates Heating/cooling properties of water moves energy around through the atmosphere Causes winds, storms, and even hurricanes

45 Blanket of water vapor also helps to keep Earth’s surface warm
Ex: Deserts get very cold at night because they don’t have very much water vapor in the atmosphere above them to trap their heat at nighttime. We don’t get as hot during the day here in NEPA, but our night’s are warmer during the summer because of the higher level of water vapor in the atmosphere here.

46 Aquifers Layers of rock or sediment that can yield usable groundwater. The water is pumped to Earth’s surface through a well. Flows at rates of meters/year Sometimes Earth’s surface dips below the level where groundwater would be. This is where natural lakes and rivers are located.

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