Lecture 3 - Chemistry of Life and Water

Question 1

name the key properties of water

Answer 1

1. Cohesion
2. Solid water is less dense than liquid water
3. High specific heat
4. High heat of vaporization
5. water is a good solvent

Question 2

describe cohesion of water

Answer 2

cohesion - hydrogen bonds hold water molecules together

• each individual bond is weak and temporary
• cumulative effects are enormous
• responsible for many of water’s important physical properties

–> water molecules stick to other water molecules by hydrogen bonding

Question 3

describe consequences of cohesion

Answer 3

• gives rise to surface tension
• surface tension: a measure of how hard it is to break the surface of a liquid
• • water has an unusually high ST due to hydrogen bonding between the molecules at the air-water interface and to the water molecules below

Question 4

describe polarity of water

Answer 4

polar due to highly electronegative oxygen atom (overall charge is evenly distributed)

polarity allows water molecules to form hydrogen bonds with eachother.

Question 5

describe adhesion

Answer 5

water molecules stick to other polar molecules by hydrogen bonding (water to other)

Question 6

describe solid water is less dense than liquid water

Answer 6

• ice floats in liquid water because hydrogen bonds in ice are more ordered making ice less dense
• bodies of water freeze from the top down
• when water freezes it increases in volume

Question 7

Define specific heat

Answer 7

amount of energy needed to be absorbed by a gram of a substance to increase its temperature by 1C

Question 8

describe high specific heat in context of water

Answer 8

• specific heat = 1 cal/g/deg C
• water resists changing its temperature because of its high specific heat
• a large amount of energy is required to change the temperature of water
• this property has important biological and climactic consequences

Question 9

Why does water have such high specific heat?

Answer 9

• H-bonds
• when water is heated, the energy must first be absorbed to break the bonds
• only after the bonds are broken can the energy increase the movement of the water molecule
• water therefore resists temperature change

Question 10

describe high heat of vaporization

Answer 10

definition: quantity of energy needed for 1g of liquid to become gas

• allows for evaporative cooling
• -the evaporation of water from a surface causes cooling of that surface
• -water molecules with the greatest kinetic energy (heat) leave the surface as gas => remaining molecules have less kinetic energy => feel cooler

Question 11

describe “water is a good solvent”

Answer 11

• water is a versatile solvent due to its polarity
• • forms hydrogen bons readily
• water dissolves polar molecules and ions

Question 12

all living organisms are said to be _____.

Answer 12

Carbon-based

Question 13

why are all living organisms said to be carbon-based?

Answer 13

all the biomolecules that form our cells are composed of a carbon skeleton

of all the chemical elements, carbon is unparalleled in its ability to form molecules that are large, and varied, making possible the diversity of organisms that evolved on Earth.

Question 14

What makes carbon so special?

Answer 14

a carbon atom can form 4 covalent bonds

• that means each carbon atom can act as an intersection point from which a molecule can branch off in as many as 4 directions
• ability of each bond to rotate freely
• • this can give rise to different shapes

Question 15

which elements make up most of living matter?

Answer 15

hydrogen
carbon
nitrogen
oxygen