BISC 1111 Chapter Notes - Chapter 3.1-3.3: Thermal Energy, Hydrogen Bond, Ice Cube

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Samuel Mohebban 3.1-3.3 Biology Notes Exam 1
1
3.1
Water is only substance to exist in the natural environment in all three physical states of
matter
Water molecule is shaped like a V, with its two H atoms joined to the oxygen atom by single
covalent bonds
Oxygen is more electronegative than Hydrogen, so the electrons of the covalent bonds spend
more time close to O than to H (covalent bonds)
Unequal sharing of electrons and water’s V-like shape make it a polar molecule (overall
charge is unevenly distributed)
Oxygen region of the molecule has a partial negative charge and each H has a partial positive
charge
When water is in liquid form, its hydrogen bonds are very fragile. These bonds are
constantly breaking and reforming
3.2
Cohesion- Hydrogen bonds between water molecules hold the substance together
o As water evaporates from a leaf, H-bonds cause water molecules leaving the veins to
tug on molecules farther down
o the upward pull is transmitted through the water-conducting cells all the way to the
roots
Adhesion- The clinging of one substance to another.
o Adhesion of water by the H-bonds to the molecules of cell walls helps counter the
downward pull of gravity
Surface Tension- a measure of how difficult it is to stretch or break the surface of a liquid
o At the interface between water and air is an ordered arrangement of water molecules,
H-bonded to one another and to the water below. This gives water high surface
tension, making it behave as though it were coated with an invisible film
Water moderates air temperature by absorbing heat from air that is warmer and releasing the
stored heat to air that is cooler.
o Water is effective as a heat bank because it can absorb or release a relatively large
amount of heat with only a slight change in its own temperature.
Kinetic Energy- The energy of motion. Anything that moves has kinetic energy
o Atoms and molecules always have kinetic energy because they are constantly
moving. Faster a molecule moves, the more kinetic energy
Thermal Energy- The kinetic energy associated with the random movement of atoms or
molecules
o The total thermal energy depends in part on the matter’s volume
o Thermal energy in transfer from one body of matter to another is defined as heat
Temperature- is a measure of energy that represents the average kinetic energy of the
molecules in a body of matter, regardless of volume
Whenever two objects of different temperature are brought together, thermal energy passes
from the warmer to the cooler object until the two are the same temperature
o Molecules in the cooler object speed up at the expense of the thermal energy of the
warmer object
o Ice cube cools a drink by absorbing thermal energy from the liquid as the ice itself
melts
Calorie (cal)- Is the amount of heat it takes to raise the temperature of 1g of water by 1° C
o Unit of heat 1 cal = 4.184 J
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Samuel Mohebban 3.1-3.3 Biology Notes Exam 1
2
Kilocalorie (kcal)- is the quantity of heat required to raise the temperature of 1 kilogram (kg)
of water by 1° C
o Unit of heat
Joule (J)- One J = .239 cal
o Unit of energy
Specific Heat- as the amount of heat that must be absorbed or lost for 1 g of a substance to
change its temperature by 1° C
o measure of how well a substance resists changing its temperature when it absorbs or
releases heat
o Specific heat of water is 1 calorie per gram and per degree.
1 cal/(g)(°C)
o Water has a high specific heat
o Ethyl Alcohol has a specific heat of .6 cal/(g)(°C)
.6 cal required to raise the temperature of 1 g of ethyl alcohol by 1° C
Specific heat of water (SH)
o High specific heat 1 cal/(g)(°C)
o Because of high SH, water will change its temperature less than other liquids when it
absorbs or loses a given amount of heat
o Water resists changing its temperature; when it does change its temperature, it
absorbs or loses a relatively large quantity of heat for each degree of change
o High specific heat can be traced to H-bonding
Heat must be absorbed in order to break H-bonds
Heat must be released in order to break H-bonds
Most of the energy used when applying 1 cal to water is to disrupt hydrogen
bonds before the molecules can actually start moving
When the temperature of water drops, many additional H-onds form,
releasing a considerable amount of energy in the form of heat
Relationship between Water’s SH and Life on earth
o cooling water can warm the air
o Water moderates air temperatures in coastal areas
o High SH of water stabilizes ocean temperatures, keeping the temperature of the water
that covers Earth within limits that permit life
o Because organisms are mostly made up of water, they are better able to resist
changed in their own temperature
Evaporation/Vaporization- the formation from a liquid to a gas
o Molecule move too fast to attract to one another, thus leaving the liquid state and
entering the gas or vapor state
o Evaporation occurs at any temperature.
o Glass of water will eventually evaporate at room temperature, but slower to that of a
glass that is heated.
o If a liquid is heated, the average kinetic energy of molecules increases (temperature),
making the liquid evaporate more rapidly
Evaporative Cooling
o As a liquid evaporates, the surface of the liquid that remains behind cools down
(temperature decreases). This occurs because molecules with the greatest kinetic
energy are most likely to leave as a gas.
o Evaporation of sweat from human skin cools down the body
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