1. PROPERTIES OF WATER

2. WATER AND HYDROGEN BONDING
PROPERTIES OF WATER
WATER AND HYDROGEN BONDING

3. WATER AND HYDROGEN BONDING
PROPERTIES OF WATER
WATER AND HYDROGEN BONDING

4. PROPERTIES OF WATER

5. PROPERTIES OF WATER
Water Ice

6. PROPERTIES OF WATER DENSITY
The density of a substance is a measure of the amount of mass that is contained in a certain volume of that substance.
It is calculated by using the formula d = m/v
(where m is the mass of the substance and v is its volume).
Typical units are g cm−3 and kg m−3.
The official symbol for density is ρ, although d is still commonly used.
The density of water varies across its three states due to expansion and contraction and this depends on its temperature.
Water’s maximum density not at its freezing point but at 4 °C.
This means that water that is approaching 0 °C, and is therefore close to freezing, floats to the top as it is less dense than the surrounding water.
The second is that ice has a density that is significantly less than water at the temperatures shown.
This is the reason that ice floats on water.
The fact that water freezes with a layer of ice across the top is attributable to both these properties.
The water that is about to freeze is at the surface and, when it does turn into ice, its lower density keeps it there.
The layer of ice that forms then acts as an insulator, preventing the water below from freezing.
This means that aquatic life can survive, even in sub-zero conditions. If ice were denser than water, some bodies of water would freeze solid during winter and the aquatic life would die.

7. THE PHYSICAL PROPERTIES OF WATER
Water is a polar, discrete molecular compound. At 25 °C, water is a colourless, odourless liquid.
It freezes at 0 °C and boils at 100 °C.
It is found in all forms —solid, liquid and gas.
Water has many properties that have resulted in the development of life on Earth in the form that we know it.
For example, it needs a great deal of energy to heat up (having both a high melting temperature (0 °C) and a high boiling temperature (100 °C) ), and it holds heat longer than most other substances.

8. SPECIFIC HEAT CAPACITY
PROPERTIES OF WATER
SPECIFIC HEAT CAPACITY

9. THE PHYSICAL PROPERTIES OF WATER
Specific heat capacity
The specific heat capacity of a substance is the amount of energy needed to raise the temperature of one gram of the substance by one degree Celsius.
The formula
follows from this definition,
where q is the energy required (in J)
to raise m g of a substance of specific heat capacity C
by ΔT degrees Celsius.

10. PROPERTIES OF WATER
The latent heat of fusion of water is the amount of energy needed to change a fixed amount of water from a solid to liquid phase at 0 °C. The bonds
between the ice molecules must be broken so that the water molecules can move around more freely in a liquid state. The latent heat of fusion of water
is 6.02 kJ mol–1, so 6.02 kJ of energy must be supplied to change each mole of water from solid to liquid.
kJ mol–1 -= kilojules of energy per mole
The latent heat of vaporisation of water is the amount of energy needed to
change a fixed amount of water from a liquid to a gas at 100 °C.
The remaining forces holding the water molecules together must be overcome
so that the molecules may move around freely as a gas.
The latent heat of vaporisation of water is 44.0 kJ mol–1,
which means that 44.0 kJ of energy must be supplied to vaporise
one mole of water.

11. PROPERTIES OF WATER
The relatively high latent heat of vaporisation of water is very useful in keeping organisms cool through perspiration.
In humans, when a person perspires, droplets of liquid water on the skin evaporate by absorbing heat energy from the body.
This change from liquid water to water vapour requires a large amount of heat energy, making perspiration an efficient mechanism for removing unwanted heat from the body.
If there is already a lot of water vapour in the air (as is the case when humidity is high), this evaporation process is slow with the result that people often feel hot and uncomfortable on such days.
We store large amounts of water in dams and lakes and because of water’s relatively high latent heat of vaporisation it evaporates more slowly than many other liquids meaning that losses due to evaporation from water surfaces are low.

12. PROPERTIES OF WATER ELECTRICAL CONDUCTIVITY
A substance conducts electricity only if it contains charged particles that are able to move.
The covalent bonding in water, which results in the formation of neutral molecules,
means that it should not conduct electricity — even though these
molecules move freely in the liquid state.
Pure water does conduct electricity very slightly.
The amount is so tiny that it is still often described as a non-conductor.
The reason for this is the ability of water molecules to react slightly with themselves
to form a small number of ions.
This is called the self-ionisation of water.
The equation for this reaction is:
H2O(l) + H2O(l) H3O+(aq) + OH−(aq)
The small extent of this reaction means that only a few ions are formed and the resulting conductivity is virtually zero. Everyday (tap) water is never pure, but contains other substances dissolved within it. Often these substances are ionic or react to form ions in the water.
Once such ions are present, the water conducts freely as the charged particles are able to move.