Properties of Water Flashcards
Heat Capacity
a measure of a substances capacity to absorb and store heat energy
Heat capacity of water
4.18J*C
Specific heat capacity
measures the amount of energy needed to increase the temperature of a certain amount of a substance by 1*C
Symbol: C
Why is the heat capacity of water high?
-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
Heat energy calculations
q=Cm△T
△T
T2-T1
Change in temperature
List the physical properties that make water unique
-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
Explain the significance of polarity and hydrogen bonding in relation to these properties of water
-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
Explain why a water molecule can form up to four hydrogen bonds with other water molecules
2 H atoms (slightly electro positive)
1 O atom (2 lone pairs can bond to 2 other hydrogen atoms)
Why is it that water doesn’t follow the trend of the other group 16 hydrides
water has a significantly higher boiling point than the other compounds due to hydrogen bonds
describe a force that must be overcome in order for ice to melt
Distribution of hydrogen bonds is almost tetrahedral in shape so molecules occupy more volume. intermolecular forces must be overcome
Explain why ice is less dense than liquid water
each water molecule forms hydrogen bonds to 4 others and the molecules are more widely spread.
therefore, ice is less dense and floats
Latent heat
the heat energy required to change the state of a substance without changing the temperature
latent heat values (L)
Latent heat of fusion
the heat needed to change 1 mole of the substance from a solid to a liquid at its melting point
latent heat of vaporisation
the heat needed to change 1 mole of the substance from a liquid to a gas at its boiling point
Latent heat of fusion of water
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)
Latent heat of vaporisation of water
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)
Significance of waters latent heat of vaporisation
-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)
latent heat formula
q=nL
amount of substance in mollatent heat value
