properties of water ocean motions governed by fundamental physical laws of conservation of mass,...

Properties of Water

Ocean motions governed by fundamental physical laws of conservation of mass, momentum and energy

Water’s truly unique property as related to Earth System Science:

At standard pressure, water changes from a liquid to a solid at 0° C (32°F) and from a liquid to a gas at 100°C (212°F). Only substance that can exist in all three phases within the Earth’s range of temperatures.

Other properties of water (additional properties in Table 7.2):

- great heat storage ability

- little internal friction

- dissolves solids and gases readily (“universal solvent”)

- changes phase in atmosphere and in ocean

- solid form floats

- transparent to some wavelengths of light, nearly opaque to others

- high surface tension

Geography 104 - “Physical Geography of the World’s Oceans”

Question:Why does water behave the way it does?

Answer:Water’s properties are due to its unique molecular structure.

Chemistry 101

- protons, electrons and (usually) neutrons form atoms- atoms, building blocks of matter, bond to form molecules- hydrogen (H) and oxygen (O) bond to form water (H2O)

Chemical bonding involves electrons- ionic bond involves transfer of electrons- covalent bond involves sharing of electrons

water molecule

covalent bonds between oxygen and two hydrogen atoms

oxygen attracts electrons more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom.

hydrogen bonds

Electrical attraction between molecules

freshwater density vs. temperature

surface tension

surface tension

Physical implications of surface tension: - capillary waves - viscosity (thickness or internal friction)- molecular diffusion

day-night temperature differences on earth’s surface

Energy is necessary to drive ocean processes.

Forms of energy important to oceanographers (Table 7.1) - solar energy- thermal energy- kinetic energy- potential energy- chemical energy

How does water store and exchange thermal energy or heat?- heat capacity - relationship between heat and temperature- temperature - measure of average kinetic energy of molecules- heat - spontaneous transfer of energy from a high temperature system to a lower temperature system

specific heat - (Cp) amount of heat necessary to change the temperature of a unit mass by 1 °C

James Joule (1818 – 1889)heat gain equivalent to potential energy loss

joule (J) – energy from a force of 1 Newton moving through distance of 1 meter

specific heat values

water = Cp(T,P) ~4180 J kg-1 °C-1

seawater = Cp(T,S,P) ~4000 J kg-1 °C-1

silicon (sand) = ~710 J kg-1 °C-1

concrete = ~752 J kg-1 °C-1

air = ~1000 J kg-1 °C-1

ice = ~2050 J kg-1 °C-1

sea breeze – as land warms to temperature greater than ocean during day

land breeze – as land cools to temperature lower than ocean during night

specific heat differences between ocean and land influences local weather

water structure and phase transitions

Heat must be added/removed to alter hydrogen bonds and change state of water. This heat not expressed in a change of temperature.

2. /

energy and phase transitions

Figure 7-11 in text; another error

3. /

0. Energy to heat 1 gm ice by 1 °C = 2.05 J/g

Readings for next time (thermodynamics of water):

Read first part of Chapter 7 (pgs 113 – 122)