BIOL 1010 Lecture Notes - Hydrophile, Evaporative Cooler, Hydrogen Bond

18 views5 pages
12 Oct 2012
Role of water
Water is the basis of life
- Life on earth probably evolved in water
- Living cells are 70-95% H2O
- Water covers about ¾ of the earth
- In nature, water exists in all three physical states of matter- solid, liquid and gas.
- It can be quite correctly argued that life exists on earth because of the abundant liquid water
- Other plants have water, but it is either gas (Venus) or water (Mars)
- Recent studies of Mars reveal the presence sometime in the past of running fluid, possibly
Polarity of water
- Water is a polar molecule. Its polar bonds and asymmetrical shape give water molecules
opposite charges on opposite sides
- 4 valance orbitals of O point to corners of a tetrahedron
- Two corners are orbitals with unshared pairs of electrons and weak negative charge
- Two corners are occupied by H atoms which are in polar covalent bonds with O.
- Oxygen is also electronegative, that shared electrons spend more time around O causing a weak
positive charge near H’s.
- Hydrogen bonding orders water into a higher level of structural organization.
- The polar molecules of water are held together by hydrogen bonds.
- Positively charged H of one molecule is attracted to the negatively charged O of another
- Each water molecule can form a maximum of 4 hydrogen bonds with neighboring water
- Water has extraordinary properties that emerge as a consequence of its polarity and hydrogen-
bonding. Come of these properties are that water:
o Has cohesive behavior
o Resists changes in temperature
o Has a high heat of vaporization and cools surfaces as it evaporates
o Expands when it freezes
o Is a versatile solvent
- Water is a polar molecule (having both a positive and negative side)
Hydrogen bonds
- Consequently, water has a great connectivity of individual molecules, which is caused by the
individually weak hydrogen bonds that can be quite strong when taken by the billons
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in
Cohesion of water molecule
- Collectively, the hydrogen bonds hold the substance together- a phenomena called cohesion.
- Cohesion contributes to the transport of water against gravity in plants. Adhesion of water to
the walls of the vessels helps counter the downward pull of gravity.
- Water has a great surface tension. At interface between water and air, hydrogen is bounded to
one another and to the water below.
Water moderates temperatures on Earth
- Water absorbs heat from the warmer air and releases the stored hear to the cooler air.
- Everything that moves has kinetic energy. The faster a molecule moves, the greater Ek.
- Heat is a measure of the total quantity of Ek due to molecular motion in a body of matter.
- Temperature measures the intensity of heat due to average Ek of the molecules.
- When the 2 objects are brought together, molecules in the cooler object speed up at the
expense of the Ek of the warmer one.
- A calorie is the amount of heat energy required for raising the temperature of 1g of water by 1
degree Celsius.
- Conversely, one calorie is the amount of heat given by 1 g of water releases when it cools down
by one degree Celsius.
Water’s high specific heat
- Water has a high specific heat, which means it resists temperature changes when it absorbs or
releases heat.
- The specific heat of a substance is defined as the amount go heat that must be absorbed or lost
for 1 g of that substance to change its temperature by 1 degree Celsius.
- The specific heat of water is 1 calorie per gram per degree C, abbreviated as 1 cal/g/C
- It is unusually high when compared to other substances, (0.6 for alcohol).
- As a result of hydrogen bonding water molecules, it takes a relatively large heat loss or gain for
each 1 degree change in temperature
- Hydrogen bonds must absorb heat to break, and they release heat when they form
- Much of the absorbed heat energy is used to disrupt hydrogen bond s before water molecules
can move faster (increase temperature)
- A large body of water can act as a heat sink, absorbing heat from sunlight during the day and the
summer (while warming only a few degrees) and releasing heat when the night and winter as
the water gradually cools.
- As a result
o Water, which covers ¾ of the planet keeps temperature fluctuations within a range
suitable for life
o Coastal areas have milder climates then inland
o The marine environment has a relatively stable temperature
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.