Chapter 11: Properties of Water Flashcards
What is water’s usual properties?
It expands on freezing
TWO properties of water?
- Relatively high melting and boiling temperatures, compare to other group 16 elements and other hydrides.
What can water absorb?
Water can absorb relatively large amount of heat with a correspondingly low temperature rise.
Where is water used for due to the large amount of heat it absorbs?
Uses in coolant in car radiators and evaporation of sweat cools the body and regulates body temperature.
What is the water molecule made of?
Two hydrogen covalently bonded to one oxygen atom.
What happens to water 25 degree?
It is colourless, transparent and odourless liquid.
What happens 0 degress and 100 degress?
It freezes at 0 degrees and boils at 100 degrees.
What are the properties that make water crucial for life?
Their polar nature and hydrogen bonding between the water molecules.
What type of intermolecular BOND is water?
Diperson force ( quite weak) and hydrogen bonding - attract each other very closely ( big three and hydrogen )
why is it dipole
Due to different electronegativites of the atoms in H2O..
Charge for water molecule?
Atom gaining greater share of bonding electrons ( delta negative = oxygen.
Low electronegativity ( hydrogen ) becomes positively charges/ Delta positive.
What do the differences in charge in the ends of a molecule produce?
A polar molecule.
What happens with the more stronger electrostatic attraction?
The closer the molecules become, and the stronger the resulting intermolecular bonds.
What does hydrogen bonding significantly affect?
Melting and boiling points and other physical properties of many compounds - such as water.
What does melting and boiling point depend on?
The strength of the intermolecular bonding between the molecules.
What is needed to break water bonds?
More heat is needed to let the molecule gain sufficient kinetic energy and to break free of the hydrogen bonding.
WHAT is boiling point?
Temperature to change from liquid to gas. Thus the input of energy is required to cause this change of state.
Endothermic?
LIQUID -> GAS
Process enabling the molecules to gain sufficient energy to break the intermolecular bonds. this the stronger the intermolecular bond, the higher the boiling temp.
Why the process of exothermic?
LIQUID -> SOLID
Water molecules in liquid state has more energy and move quickly than water molecule in ice. To change state from liquid to ice, energy MUST BE REMOVED.
process of exothermic?
LIQUID -> SOLID
water to ice
- temp decreases due to energy being removed
- molecule starts to move slowly
- forms a crystalline lattice ( usually in bonds of tetrahedral arrangements. )
Why does ice float on water?
Since water expands on freezing, it is less dense as a solid.
ARRANGEMENT OF ICE
all bonded ( oxygen to hydrogen - in a hexagon shape )
ARRANGEMENT OF WATER
Slightly bonded ( dotted lines ) , spread out . forms hydrogen bonding like a tetrahedral.
ARRANGEMENT OF STEAM
Seperate bonds
Energy input
- In ice?
- In water?
- melts …. Water
- boils….. Steam
Energy Output
- In steam?
- In water?
- condense…. water
- freezes….. ice
What is density?
The measure of the amount of mass that is contained in a certain volume of that substance.
How is density calculated?
units??
d= m/v
m= mass
v=volume
UNITS ARE:
gmL power of neg 1
kg m power of neg 1
Quick 2 features of water?
POLAR
Hydrogen-oxygen bonding = hydrogen bonding between water molecules.
Does density of water always stay the same?
No, it varies according to state such as expansion and contraction = which all depends on water temperature.
BASED ON GRAPH
lower the temp of ice (0, -40, -50)
The higher the density (but only by 0.01)
BASED ON GRAPH
lower the temp of water ( 2, 0)
The higher the density (p) usually yet various among
not too important info
What is water’s highest density (max) ?
At 4 celcius which is 0.999 98
What has the higher density?
Ice has less density than water ( up to -50 temp)
Thats why ice floats on water
graph
- –4c ——–
- - ——- dsty slwly incre as heat removed- ——- ice water ——-
Water’s usual propety?
Its solid form (ice) is less dense than its liquid form.
THATS WHY when water freezes a layer of ice is on top
What does it mean when ice forms a hexagon?
Ice floats on water and then water freezes from the surface down.
What is the purpose of the layer of ice that forms on water?
Insulator, preventing the water below from freezing, and aquatic life to survive in sub-zero conditions.
Explains why bottles cracks when frozen.
Decreases in density from liquid to solid water means ice volume of ice is greater than the corresponding volume of water.
What group is water?
H2O is in group 16 hydrides
Group 16 trend?
If water is avoided, the obvious trend is increasing temperature within the group.
The larger the molecule, the higher the melting and boiling temp. H20 IS OBV the strongest bond.
Why does water have a higher boiling point other group 16 hydrides?
Water’s hydrogen and oxygen- a very strong dipole called hydrogen bond.
Weakest to strongest bonds
Dispersion forces
Dipole-dipole dorces
hydrogen bondign
Covalent bonding
Describe the structure of water
Has two hydrogen covalently bond to one oxygen
Two lone pairs and repulsion of lone pair and bonding pair creates a bend.
Why is water described as polar?
The ends of the molecules has a different charge of electronegativity ( one slightly neg and pos )
creating polar covalent bond, also has bent meaning uneven charge distributed overall.
Changing state from gas to liquid is?
An exothermic because energy has to be removed since gas has higher kinetic energy than liquid.
condensation
Are covalent bonds or hydrogen bonds are broken when liquid water evaporates into steam?
Yes the intermolecular hydrogen bonds are broken
but the covalent bonds between the atoms in the molecule are still intact.
Is density of water at 5c higher or lower than density of water at 25c?
It is higher since it is closer to the highest amount of density water can reach - which is 4.
Explain why ice floats?
When water freezes = density decreases since it loses energy and becomes hexagonal crystallined lattice
occupies more volume than random arrangement of molecules in liquid form.
Intramolecular force & Intermolecular forces diff
Intramolecular forces are the forces that hold atoms together within a molecule.
Intermolecular forces are forces that exist between molecules.
Waters Intramolecular force & Intermolecular forces
Intramolecular: covalent bonding
Intermolecular: hydrogen bonding
Melting point of H20 and comparison of other elements in group 16.
100c temp ( highest ) while every element bonded to hydrogen is lower
Boiling point of H20 and comparison of other elements in group 16.
0 c temp ( highest ) while every element bonded to hydrogen is lower
Lower the electronegativity diff =
less polar
What is latent heat?
NO CHANGE IN TEMP IF A GRAPH
Energy needed to change state (melting or boiling temp)
Why is it called latent or hidden heat?
When water changes states,
its temp remains constant = no change occurs in kinetic energy of h20 molecules
the energy goes to or comes from (endo exdo ) potential energy stored in the hydrogen bonds between the molecules.
Latent heat of water summary
Energy is needed to break the bonds between the water molecules. This causes the temp to remain constant even though the water is being heating.
Example of Latent heat on water
Ice melting = energy supplied to break bonds between molecules and the temp
.. only begins to rise again once the change of state is complete.
Latent heat symbol
L
Common units for latent heat
kJ mol ^ neg 1.
J kg ^ neg 1
What is Latent heating of fusion (L down f )?
Energy needed to change a fixed amount from the solid to the liquid (state.) phase at 0 c
process of Latent heating of fusion
Solid to liquid phrase at 0c, the latent heat of fusion required to break the hydrogen bonds between the ice molecules in the crystal lattice.
6.02 kJ energy must be supplied to change each mole of water from solid to liquid.
Number of kJ is Latent heating of fusion?
6.02kJ mol ^ neg 1
thus 6.02 kJ energy must be supplied to change each mole of water from solid to liquid.
What is Latent heating of vaporisation (L down v )?
Energy needed to change a fixed mass from the liquid to the gaseous (state) at 100c.
process of Latent heating of vaporisation
Change in liquid to gas at 100c, energy required (Latent heating of vaporisation) breaks remaining forces holding the water molecules together, allowing the molecules to move around freely as gas.
What energy is greater Latent heating of fusion or vaporisation?
vaporisation IS GREATER because molecules must be completely separated from each other when changing liquid –> gas and not just slightly moved apart when moving from crystal lattice in ice to liquid water.
EXAMPLE OF USING HEAT FROM BODY IRL
Sweating uses heat from the body to evaporate the moisture.
Number of kJ is Latent vaporisation of fusion?
40.7 kJ mol ^ neg 1
thus 40.7 kJ energy must be supplied to vaporise one mole of water
What is relatively high latent heat of vaporisation of water very useful for?
Keeping organisms cool through perspiration. Person sweats, change from liquid water to water vapour needs alot of heat energy.
This energy is absorbed from our body, making perspiration an efficient mechanism for removing unwanted heat from the body.
Plus humid air helps too but slow process.
The higher the latent heat of a substance…
greater the amount of energy needs when it changes states.
Water is an exception due to its size for amount of latent heat required cause
It has higher due to strong intermolecular forces within its solid and liquid state.
water evaporates slowly than other liquids.
Heat required to change state equation
q = n x L
q= heat energy required or released kJ n= no. of mole of substance L= latent heat
What is specific heat capacity?
Energy measure in joules, needed to raise the temperature of 1g of a pure substance by 1 c.
What is specific heat capacity measure of?
How easy or difficult it is to change the temp of a substance.
What does it mean by water has a high specific heat capacity?
give real life example
Temp is difficult to alter. That’s why the beach is popular hot days, as water can absorb heat from its warmer surroundings so that the air temp by the seashore is lowered.
Equation for energy specific heat capacity ( energy required to raise the temp of a particular mass of a substance )
q = mc delta T
q= energy required in joules
m= mass in grams
c= specific heat capacity of the substance
delta t= temp change
Why does water have a high specific heat capacity?
Due to large amount of hydrogen bonding between water molecules. Thus water is a good insulator of heat.
Water can absorb large amounts of heat energy with only a minimal increase in temperature.
Water’s specific heat capacity?
4.18 J g ^ neg 1 celcius ^ neg 1
What is the name of the energy that change liquid to gas and vice versa without any change in temperature?
Latent heat of vapourisation
Heat energy is continually supplied to keep water boiling at 100c. Why does temp stay constant?
The heat energy is used to break the intermolecular hydrogen bonds between the water molecules while the temp remains constant.
Explain what it means when we say water has a specific heat capacity of 4.18J g^neg 1 cel^1
The energy, measured in joules needed to raise the temp of 1 g of water by 1 c is 4.18 J.
On a hot day the sand feels warm but the sea is cold.
Why is that?
Water has higher specific heat capacity than sand so it requires more heat energy to raise its temp. This means the temp of the sand increases at a faster rate than that of the water.
What is responsible for the expansion of water in the solid state?
The ordered arrangement of water molecules into a crystalline lattice structure.
This is because water expands upon freezing.
Why can marine life survive in winter?
Density of ice is less than liquid water, thus ice floats on water due to its lower density, providing an insulating layer that prevents the water below from freezing.
Ice floats on top, trapping oxygen below, if ice was denser than water, it would freeze bottom up.
How water create relatively stable environment for ocean organisms.
Water absorb high amount of heat from the atmosphere with a minimal increase in temp assists in maintaining a relatively stable environment for ocean organisms.
Boiling temp
liquid to vapour
Hydride
Binary compound containing hydrogen
Melting temp
solid to liquid
What is the hydrogen bonding in water an example of?
Intermolecular bonding ( bonds between molecules )
Ice is a crystalline lattice of molecules.
The bonding that holds the water molecules in the lattice together is best described as?
Dispersion forces and hydrogen bonding.
Two solids have different masses but the same volume.
The solid with the lower mass..
has a lower density.
Cells contain mainly water. If lettuce leaves are placed in the freezer and then defrosted, they come soft and soggy.
Explain why.
When lettuce leaf is frozen the water in its cell expands and breaks the cell walls.
Cell loses its shape, leaving the lettuce limp when defrosted.
Why does boiling point of group 16 hydrides decrease and then increase?
Water has highest BP AND MP temp cause of hydrogen bonding.
Other group hydrides depend on dispersion forces, which are weak, but increase as size of molecule increases.
Why is it more dangerous to receive a burn by steam at 100c than one by water 100c.
Steam has all the molecules spread out more, while water has high SHC so it takes..
Why is water different from most liquids
- mention density in solid and liquid states
- Substances becomes denser as temp decreases until a solid is formed
- Water has lower density in the solid form as more ordered regular arrangement of molecules in the solid form compared to liquid form.
- ordered arrangement takes up less space so density is less.
How does water have usual physical property
- Relatively high SHC
- Capable of absorbing large amount of heat before its temp rises significantly
Used as coolant in car keep engine from overheating
Why does tumble dryers use so much electricity to dry clothes?
- Large amount of energy to evaporate water
- Water’s high latent heat of vaporisation
What happens to density of water as temp decreases.
Density of water increases as temp decreases, until max density 4c cause water molecules start to form hexagon crystalline lattice in ice, held together by hydrogen bonding, instead of closer arrangement found in water.
In an experiment if volume has increases…
density has decreased.
Damp clothes around water bottle to cool down..
Damp cloth absorbs heat energy from bottle to evaporate/change state , keeping water inside cool
Water droplets on the side of a can from fridge
Water vapour from air condenses, when contact with cold can. Energy goes into the can from the water in the condensation process
cohesion
water molecules stick to each other
surface tension of water
adhesion
water molecules sticks to other substances
cohesion & adhesion happen?
due to polar nature
