BIO 120 Lecture Notes - Lecture 3: Kinetic Energy, Thermal Energy, Hydrogen Bond
Bio 120- Chapter 3: Water and Life
★Polar covalent bonds: electrons of the covalent bonds spend more
time closer to oxygen
★Polar molecule: the unequal sharing of electrons, overall charge is
unevenly distributed.
★Water: The partially positive hydrogen of one molecule is attracted
to the partially negative oxygen of a nearby molecule. The two
molecules are thus held together by a hydrogen bond.
★Four properties of water
○Cohesion of water molecules
■Water molecules stay close to one another due to
hydrogen bonding
■Cohesion: hydrogen bonds hold the substance together.
Contributes to the transport of water and dissolved
nutrients against gravity in plants.
■Adhesion: clinging of one substance to another. Helps
counter the downward pull of gravity.
■Surface tension: measure of how difficult it is to stretch
or break the surface of a liquid. Water has an unusually
high surface tension.
○Moderation of Temperature by Water
■Water absorbs heat from air that is warmer and releasing
the stored heat to air that is cooler.
■Temp and heat:
●Kinetic energy: the energy of motion. The faster
molecules moves, the greater the energy.
●Thermal energy: the kinetic energy associated with
the random movement of atoms or molecules.
Total kinetic energy, depends on volume.
●Temperature: average kinetic energy of the
molecules in a body of matter, regardless of
volume.
●Heat: thermal energy in transfer from one body of
matter to another
●calorie(cal): amount of heat it takes to raise the
temp of 1 g of water by 1 degree C.
●Kilocalorie (kcal): 1,000 cal is the quantity of heat
required to raise the temp of 1 kg of water by 1
degree C.
●Joule (J): 1 J= .239 cal; one cal= 4.184 J
○Specific High Heat: ability of water to stabilize temp stems
from relatively high specific heat.
■Amount of heat that must be absorbed or lost for 1 g of
that substance to change its temp by 1 degree C.
■Water will change its temp less than other liquids when
it absorbs or loses a given amount of heat.
■Specific heat: a measure of how well a substance resists
changing its temperature when it absorbs or releases
heat.
■Heat must be absorbed in order to break hydrogen
bonds; heat is released when hydrogen bonds form.
○Evaporative Cooling
■Molecules moving fast enough to overcome these
attractions can depart the liquid and enter the air as a
gas.
■Transformation from a liquid to a gas= vaporization or
evaporation
■If a liquid is heated, the average kinetic energy of
molecules increases and the liquid evaporates more
rapidly
■Heat of vaporization: is the quantity of heat a liquid
must absorb for 1 g of it to be converted from the liquid
to the gaseous state
■Evaporative cooling: As a liquid evaporates, the surface
of the liquid that remains behind cools down (its
temperature decreases)
★Water: the Solvent of Life
○Solution: a liquid that is a completely homogeneous mixture
of two or more substances
○Solvent: dissolving agent of a solution
○Solute: substance that is disabled
○Aqueous solution: solute is dissolved in water; water is the
solvent. water is a versatile solvent
○Hydrophilic and hydrophobic substances
Document Summary
Polar covalent bonds: electrons of the covalent bonds spend more time closer to oxygen. Polar molecule: the unequal sharing of electrons, overall charge is unevenly distributed. Water: the partially positive hydrogen of one molecule is attracted to the partially negative oxygen of a nearby molecule. The two molecules are thus held together by a hydrogen bond. Water molecules stay close to one another due to hydrogen bonding. Cohesion: hydrogen bonds hold the substance together. Contributes to the transport of water and dissolved nutrients against gravity in plants. Adhesion: clinging of one substance to another. Surface tension: measure of how dif cult it is to stretch or break the surface of a liquid. Water absorbs heat from air that is warmer and releasing the stored heat to air that is cooler. The faster molecules moves, the greater the energy. Thermal energy: the kinetic energy associated with the random movement of atoms or molecules.
