water 5

Slide1: 

Water - the Earth’s Coolant

Slide2: 

Put this in your notes: The Earth’s energy is solar. Incident light from the Sun heats the surface. Water’s high heat capacity allows it to absorb or give up this energy without much temperature change. Circulation in the ocean and atmosphere redirects energy from regions of excess (tropical zones to regions of deficit (polar zones), moderating temperatures in both.

Slide3: 

Now, let’s explain this process! Water is the Mickey Mouse molecule: hydrogen has one proton(+) and one electron (-) oxygen has 8 protons and 8 electrons

Slide4: 

+ - Water is a polar molecule (one end is more negative and the other is more positive).

Slide5: 

Why should I care??!! H and O from different molecules form weak bonds (hydrogen bonds) that make water a liquid. Why do you think the polar nature allows this to happen?

Slide6: 

The polar nature of water also makes it a VERY good dissolver (THINK: what do you do with a really yucky pan- soak it overnight!) This polar nature also makes water wet- it adheres (sticks) well to things

Slide7: 

What else can we blame on water’s polar nature?….. Water’s ability to absorb heat energy without a big rise in temperature! …or give up heat without a big drop in temperature) Let’s look at heat and temperature: (… there is a difference, you know!)

Slide8: 

Solids have low enough energy that molecules can form rigid bonds. Gases have such high energies that the molecules cannot form bonds. Transitions between states take place by adding or removing energy. Heat is the energy of molecular vibration. Temperature is a measure of that energy.

Slide9: 

Heat capacity is how much heat one gram of a material can absorb before its temperature changes by 1°C. Water has one of the highest heat capacities of any known substance. This is because the hydrogen bonds in liquid water are strong enough that lots of heat (vibrational) energy is required to break these bonds, (and remember, the hydrogen bonds are a consequence of the polar nature of water.

Slide10: 

This is why beaches are HOT and the surf is COOL! … even though both get the same solar heat.

Slide11: 

More weird properties of water…. Water is the only substance with a solid density less than its liquid.

Slide12: 

E-D - all ice, adding heat raises temperature of ice to 0°C (melt point) D-C - ice + liquid water, constant T because all heat going to melt ice C-F - all liquid, heat raises temperature of water by 1°C for each calorie added per gram. F-G - liquid + vapor, water boiling, constant T because heat added goes to breaking H bonds and allowing molecules to escape (boil)

Slide13: 

Ice melting gives up almost as much heat energy (80 calories) as it takes to raise the temperature of 1 gram of water from freezing temperature (0) to boiling (100°C).

Slide14: 

.. and it takes over 5 times as much (540 calories) heat to boil a gram of water!

Slide15: 

Note: Fog is NOT water vapor. It is made of tiny droplets of liquid water that have condensed in the atmosphere from vapor. This vapor has given up its 540 cal/gram of energy to form the droplets (warming the air).

Slide16: 

Why is this important to you? 1. In hot climates, evaporating water absorbs LOTS of heat energy that could go to heating you up! (the water in your perspiration gets some of that energy from your skin, cooling you). TROPICS 2. In cold climates, freezing water gives up heat to keep the air from getting any colder than 0°C. POLAR REGIONS 3. In your cold drink, melting ice absorbs heat that could go to warming the liquid. This is why your drink stays cold!

Slide17: 

But the ocean is NOT pure water. What is the principal difference between water and seawater? It’s SALTY!! Sea water contains about 3.5% dissolved solids and 96.5% water

Slide18: 

These salts lower the freezing point of sea water to ~ -2°C because the salt interferes with lattice of ice crystals. (acts as antifreeze!) This is why we can make ice cream!! Adding salt to ice lowers the melting temperature of the mix to -2°C, but the water in the ice cream mix still freezes at 0°C. Thus, heat flows from the mix to the salty ice.

Slide19: 

Oh, yeah, there are also some important consequences for the ocean….. When sea water begins to freeze, the ice that forms is pure water and the remaining liquid is concentrated in salts. It is denser, and this cold, salty water sinks into the deep ocean. CREATES OCEAN CIRCULATION!

Slide20: 

The ocean acts as a thermal buffer: it absorbs or radiates heat in order to try to keep its temperature constant: Sahara Desert (50°C) to Antarctic continent (-90°C) on continents Ocean changes from freezing (-2 °C) to the tropics (34 °C) 140 °C 36 °C

Slide21: 

Why would Norfolk have a much larger temperature variation than San Francisco? (same solar input and both next to ocean)

Slide22: 

The ocean moderates the Earth’s surface temperature by: 1. transporting heat from the tropics where there is an excess to the polar regions where there is a deficit - currents such as the Gulf Stream 2. Melting and freezing polar ice each year (THINK: which way does the heat flow in melting and freezing) (1/3 from oceans, 2/3 from atmosphere) 3. Evaporation in tropical regions (and then transport by atmosphere elsewhere)

Slide23: 

… but not all of the ocean participates in this buffering effect! Cold, salty water is denser than warm, less salty water. What happens? Dad, dense stuff SINKS! .. and then, Bart, the cold, salty water rises… Why? GRAVITY!!!!

Slide24: 

The ocean is layered due to density differences caused by: Always temp. Sometimes salinity Surface zone - well mixed. WHY? Waves, currents Pyncocline - region of rapid increase in density Deep zone - stable density, 80% of water Involved in buffering of climate Isolated

Slide25: 

Movement between layers does not happen unless density is about the same (WHY?) Little solar heating!!

Slide26: 

Variations in sea surface temperature lead to several climatic phenomena:

Slide27: 

Salinity variations can be explained by a balance between evaporation (makes water saltier) and precipitation (makes water less salty): P>E P>E E>P

Slide28: 

What else happens in the surface, or mixed, zone? LIFE!! Life requires LIGHT - photosynthesis is the basis of life for most of the planet. … but how deep does light go?

Slide29: 

Photic zone Little light penetrates to below photic zone and it is blue (hydrogen bonds in water absorb red light)

Slide30: 

What you see: What you photo with a strobe: (only blue light)

Slide31: 

The effects of density, temperature, and salinity layering affects provides places for submarines to hide….

Slide32: 

Rule for refraction: sound bends towards low velocity