Properties of Water

Question 1

Heat Capacity

Answer 1

a measure of a substances capacity to absorb and store heat energy

Question 2

Heat capacity of water

Answer 2

4.18J*C

Question 3

Specific heat capacity

Answer 3

measures the amount of energy needed to increase the temperature of a certain amount of a substance by 1*C
Symbol: C

Question 4

Why is the heat capacity of water high?

Answer 4

-The presence of hydrogen bonds between water molecules
-hydrogen bonds are stronger than other intermolecular forces so they are able to absorb large amounts of heat energy before they break

Question 5

Heat energy calculations

Answer 5

q=Cm△T

Question 6

△T

Answer 6

T2-T1
Change in temperature

Question 7

List the physical properties that make water unique

Answer 7

-Relatively high melting and boiling point
-high heat capacity
-high latent of fusion and evaporation for a substance of its molecular size
-decreases in density on freezing

Question 8

Explain the significance of polarity and hydrogen bonding in relation to these properties of water

Answer 8

-H-O bond is highly polar, so hydrogen bonds exist between water molecules
-Hydrogen bonds are stronger and require more energy to break than other intermolecular bonds (which is why there is a high boiling and melting points)
-Hydrogen bonds in ice results in open arrangement of molecules, so ice is less dense

Question 9

Explain why a water molecule can form up to four hydrogen bonds with other water molecules

Answer 9

2 H atoms (slightly electro positive)
1 O atom (2 lone pairs can bond to 2 other hydrogen atoms)

Question 9

Why is it that water doesn’t follow the trend of the other group 16 hydrides

Answer 9

water has a significantly higher boiling point than the other compounds due to hydrogen bonds

Question 10

describe a force that must be overcome in order for ice to melt

Answer 10

Distribution of hydrogen bonds is almost tetrahedral in shape so molecules occupy more volume. intermolecular forces must be overcome

Question 11

Explain why ice is less dense than liquid water

Answer 11

each water molecule forms hydrogen bonds to 4 others and the molecules are more widely spread.
therefore, ice is less dense and floats

Question 12

Latent heat

Answer 12

the heat energy required to change the state of a substance without changing the temperature
latent heat values (L)

Question 13

Latent heat of fusion

Answer 13

the heat needed to change 1 mole of the substance from a solid to a liquid at its melting point

Question 14

latent heat of vaporisation

Answer 14

the heat needed to change 1 mole of the substance from a liquid to a gas at its boiling point

Question 15

Latent heat of fusion of water

Answer 15

6.0kJ
this means 6.0 kJ of energy is needed to change 1 mole of water from a solid to a liquid at 0 degrees
(break some hydrogen bonds)

Question 16

Latent heat of vaporisation of water

Answer 16

44.0KJ mol^-1
this means that 44.0KJ is needed to change the state of 1 mole of water from a liquid state to a gas at 100 degrees
(break all hydrogen bonds)

Question 17

Significance of waters latent heat of vaporisation

Answer 17

-cooling system for living organisms
(sweat extracts large quantities of heat)
-longevity of water supplies
(loss of water would be far greater if low latent heat)

Question 18

latent heat formula

Answer 18

q=nL
amount of substance in mollatent heat value