Pressure

Define vapour pressure in terms of observable and measurable properties. Construct and interpret a graph of vapour pressure versus temperature. Describe vaporization at the molecular level using diagrams. Define normal boiling temperature and boiling temperature in terms of vapour pressure.

Air is a gas...it must also be exerting pressure. Pressure is defined as force per unit area. Air is a gas...it must also be exerting pressure. Called air pressure or atmospheric pressure.

The standard unit of atmospheric pressure (at sea level): 1 atmosphere = 760 mmHg = 101.325 kPa kilopascals millimeters of Mercury

Closed container (constant temperature) As liquid continues to vaporize, a point is reached: For every molecule that vapourizes, another condenses (equilibrium)

equilibrium

Pressure of gas at equilibrium with its liquid in a closed container is known as the vapour pressure. characteristic physical property

A manometer measures pressure.. Measures difference in height on both sides.

IMFs determine the rate of vapourization. Lower IMFs - faster vapourization - more particles (before equilibrium) - higher vapour pressure.

Heat increases particles kinetic energy - breaks IMF. Increases rate of vapourization - pressure increases.

Boiling – temperature remains constant. Boiling Point: vapour pressure is equal to atmospheric pressure. (1 atmosphere, 101.3 kPa, 760 mmHg)

Strong IMFs need more energy to produce gas with enough pressure to equal atmospheric pressure. Any change in air pressure will produce a change in the boiling point.

Longer cooking time to prepare foods at higher altitudes. At lower pressure the water boils at a lower temperature – longer cooking time.