Water

Question 1

what does water exist as?

Answer 1

Water exists as discrete v-shaped molecules

Question 2

what bonds does water have?

Answer 2

Water has very strong covalent bonds within the molecule, and weak dispersion and hydrogen bonds between the molecules

Question 3

what type of molecule is water?

Answer 3

Water is a polar molecule

Question 4

does water conduct electricity?

Answer 4

Pure water does not conduct electricity (no charged particles)

Question 5

what is g to mL for water?

Answer 5

1.0g of water = 1mL of water
This is often rounded to 1g = 1mL

Question 6

what states can water be found on in earth?

Answer 6

Water can be found in all 3 states on Earth

Question 7

melting and boiling pts of water?

Answer 7

Melting pt: 0oC Boiling pt: 100oC

Question 8

how much of the earth does water take up?

Answer 8

70% of the Earth’s surface is covered in water

Question 9

what is water essential for?

Answer 9

Water is essential for life

Question 10

how much of the body is water?

Answer 10

60% of the human body is water

Question 11

how does the water move through the environment?

Answer 11

Water moves through our environment in the water cycle

Question 12

how much of the earths water is fresh and readily available?

Answer 12

fresh - 3%
fresh and readily available - 1%

Question 13

define density

Answer 13

Density is how heavy something in for its size.

Question 14

formula for density?

Answer 14

Density = mass/volume

Question 15

what does lower density objects do in relation to water?

Answer 15

Lower density substances float on higher density substances (eg. oil on water)

Question 15

what is unusual about the density of water?

Answer 15

• For most chemicals, their solid state is more dense than their liquid state → solid sinks
• Water is very unusual, its solid state is less dense than its liquid state → solid floats

Question 16

what is the solid and density structure for most objects?

Answer 16

For most chemicals, solid is very tightly packed (high density), liquid is less tightly packed (lower density)

Question 17

why is solid water less dense than its liquid state?

Answer 17

• Solid water takes on a very unusual structure
• Hydrogen bonding in solid water creates hexagon structure with very large spaces
• Unusually, water expands as it goes from liquid to solid
• Water becomes less dense in its solid state

Question 18

water in relation to group 16 hydrides?

Answer 18

Water melts/boils at unusually high temps compared to other Gp 16 hydrides.

Question 19

how do waters bonds influence melting and boiling points?

Answer 19

Water forms both dispersion + hydrogen bonds between molecules. The others do not for hydrogen bonds.
NB: why does melt/boiling pt. increase for others in this Gp?
→ dispersion forces ↑ strength with ↑ molar mass

Question 20

does everything have specific heat capacity?

Answer 20

All substances have a specific heat capacity

Question 21

what is specific heat capacity?

Answer 21

This is the amount of energy (measured in joules), needed to raise the temperature of one gram of that substance by one degree

Question 22

what is waters specific heat capacity?

Answer 22

Water has an unusually high specific heat capacity. c = 4.18 J/g/oC (VCAA databook)

Question 23

what does waters specific heat capacity mean?

Answer 23

This means lots of heat energy is needed before there is much change in temperature of water.

Question 24

specific heat capacity formula?

Answer 24

q = m x c x ΔT

Question 25

what is q?

Answer 25

Energy (in Joules)

Question 26

what is m?

Answer 26

mass of water (g)

Question 27

what is c?

Answer 27

S.H.C. of substance

Question 28

what is ΔT?

Answer 28

change in temp (oC)

Question 29

benefits of water?

Answer 29

- Water is an effective insulator (it resists changes in temp better than other materials). This also means once heated, it retains heat for longer periods of time (eg hot water bottle) - Areas near water (eg beach) are cooler as the water is able to absorb large amounts of heat, energy from the surrounds, without having water temp increase much - Sweating helps cool the body by absorbing heat energy and evaporating into a gas

Question 30

what happens when a substance changes states?

Answer 30

- When a substance changes state the temperature holds constant - The temperature will not increase further until the state change is complete

Question 31

where is heat energy going when substances are changing states?

Answer 31

- During the state change, heat energy is still being supplied but it is not converted to increases in temp. - The lost/hidden energy is breaking the hydrogen bonds (and dispersion) between the water molecules

Question 32

what are the two points of latent heat for water?

Answer 32

latent heat of fusion and vaporisation

Question 33

define Latent heat (enthalpy) of fusion

Answer 33

amount of heat energy required to change 1 mole of water from (s) → (l) at 0oC

Question 34

water's Latent heat of fusion?

Answer 34

6.02 kJmol-1

Question 35

define Latent heat (enthalpy) of vaporisation

Answer 35

amount of heat energy required to change 1 mole of water from (l) → (g) at 100oC

Question 36

water's Latent heat of vaporisation?

Answer 36

40.7 kJmol-1

Question 37

does latent heat of fusion or vaporisation use more energy?

Answer 37

More energy is required for the (l) → (g) change (break all intermolecular bonds), therefore latent heat of vaporisation

Question 38

does changing water from gas to liquid to sold require energy?

Answer 38

When you start with water as gas and move through (g) → (l) → (s), energy is not required (as no bonds need to be broken). In fact these state changes form bonds, and energy will be released from the water.

Question 39

what will latent heat calculations typically use?

Answer 39

Calculations involving latent heat will generally involve using the known relationship between energy (kJ) and moles (mol) and then cross multiplying in a new situation