W a t e r

1. W a t e r

2. What is Water? • Water is a chemical substance that is essential for all life forms • It covers 71% of the Earth’s surface • Oceans hold 97% of Earth’s surface water • It is the only substance on Earth that is found abundantly in all three states (solid, liquid, gas) • Water molecules are composed of hydrogen and oxygen (H2O). • These molecules are held together by strong hydrogen bonds that allow water molecules to stick to other water molecules and many other compounds

3. Properties of Water • Water is colourless, odourless and tasteless • Water has an unusually high freezing point for its molecular mass; thus water is a liquid at room temperature, where other similar compounds would be gaseous • Water is known as the universal solvent because it can dissolve large amounts of different kinds of substances. These substances are known as hydrophilic (water-loving).

4. Properties of Water • Water has the highest surface tension of all liquids • Pure water has its maximum density at 4°C. It becomes less dense as it freezes. • Almost all substances contract when they freeze; however, water expands by 9% when it changes from water to ice.

5. Properties of Water • Water has a low viscosity, meaning it flows easily • Water is very transparent for a liquid. Only strong UV light is slightly absorbed by water • Increasing pressure raises the boiling point of nearly all solids. Increasing pressure lowers the boiling point of ice

6. Water and Heat • The change in temperature of a substance when heat is added or removed is called ‘sensible heat’ because it can be measured on a thermometer. • When a substance such as water changes states, heat is added or removed without a change in temperature. • This is called ‘latent heat’.

7. Specific Heat Capacity • The amount of heat required to raise the temperature of 1g of a substance by 1˚C • Water has the second highest specific heat capacity of all substances • Water can absorb a huge amount of heat without raising its temperature that much

8. Heat of Fusion • The amount of heat required to melt 1g of a solid into a liquid • Water has a large heat of fusion; thus it requires a large amount of energy to melt ice • When water absorbs solar energy, some of the energy is used to melt the ice and is not available to increase the temperature of the water

9. Heat of Vaporization • The amount of energy required to convert 1g of a substance from a liquid to a gas • When water absorbs solar energy, some of the energy is used to evaporate the water and is not available to increase the temperature of the water • Water vapour has a lot of energy

10. The Hydrologic Cycle • Dominated by the oceans • Shapes the weather and climate • Supports plant growth and makes life possible • A three step process

11. The Hydrologic Cycle - Accumulation • Precipitation falls on land accumulates in large pools, such as oceans, lakes, and ponds • Some water runs off into surface waters like rivers and streams (surface runoff) • Some water seeps into the soil by infiltration • Water that flows in underground steams in called subsurface runoff • Water from melting snow and ice is called meltwater runoff

12. The Hydrologic Cycle - Evaporation • Some surface water returns to the air in a gaseous form (water vapour) • Some water evaporates from the pores of plants by transpiration • Solar energy drives the evaporation of water

13. The Hydrologic Cycle - Condensation • Water vapour cools as it moves upward in the atmosphere • Vapour is converted back to liquid • Droplets form and gather as clouds • Depending on temperature, droplets will either be frozen or liquid • As clouds become oversaturated, water returns to land by precipitation and the cycle continues