Water as a Unique Chemical

Unit 2

Water on earth: nearly all water isn’t pure -

Water is a good solvent (lots of substances from the environment dissolve in it).

Boiling temp/point -

temp at which it changes from liquid to gas.

Melting temp/point -

 temp at which it changes from solid to liquid.

What does high melt/boil point depend on . Use water as an example.

These depend on the strength of intermolecular bonding between molecules.

High melt/boil point = more energy to overcome forces,and allow molecules to move apart.

E.g. water has strong hydrogen bonds

Water with freezing and heat:

Heat - molecules get more kin. energy to break hydrogen bonds.

Freezes - crystal lattice structure formed + greater volume.

Density definition

measure of the amount of mass contained in a certain volume of substance.

d=m/v

Water density

varies across states (expansion/contraction, temperature). 1mL water = mass of 0.997 g

Heat capacity

measure of substance’s capacity to absorb/store heat energy, and how much energy the substance absorbs as its temp increases.

Specific heat capacity (c)

measures amount of energy (J) to increase temperature of amount (1 gram) of the substance by 1C. 

reflects type of bonds holding molecules, ions or atoms together in substance.

Water has a higher SPC because?

(4.18Jg/C) - 4.18 joules of heat energy to increase temp of 1 gram of water by 1C. High - hydrogen bonding (can absorb, and store large amounts of heat energy before they break).

Latent Heat

energy to change fixed amount of substance (1 mole often), from solid to liquid/ liquid to gas. Symbol L - (kJ/mol).

Note: over the time that latent heat is being absorbed, the temp doesn’t change.

Latent heat of fusion

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

Latent heat of vaporisation

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

Water: Significance of Latent Heat

 cooling system for living organisms, liquid coolants, longevity of water supplies.