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)