Pressure

Define vapour pressure. Include: volatility, dynamic equilibrium Define normal boiling point in terms of vapour pressure. Interpolate and extrapolate information from pressure versus temperature graphs. Additional KEY Terms Manometer

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 = kPa kilopascals millimeters of Mercury

Closed system (constant temperature) As liquid continues to vaporize, a point is reached: For every molecule that vapourizes, one condenses When vapourization = condensation we have reached equilibrium.

dynamic equilibrium

The pressure of a gas at equilibrium with the liquid in a closed system is known as the vapour pressure. characteristic physical property

A manometer measures vapour pressure. Compares vapour pressure to air pressure. Measures difference in height on both sides.

IMFs determine the rate of vapourization. Weak IMFs: more particles vapourized - higher vapour pressure – more volatile.

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

Boiling Point: When vapour pressure is equal to atmospheric pressure. Particles must have: Energy to break IMFs Energy to push out of the liquid and through the air. (1 atmosphere, kPa, 760 mmHg)

Any change in air pressure will produce a change in the boiling point. Particles with strong IMFs require more energy (higher temperatures) to phase change to a gas with enough pressure to equal atmospheric pressure.

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

Standard air pressure is kPa. Boiling Temp Boil: when vapour pressure = air pressure

CAN YOU / HAVE YOU? Define vapour pressure. Include: volatility, dynamic equilibrium Define normal boiling point in terms of vapour pressure. Interpolate and extrapolate information from pressure versus temperature graphs. Additional KEY Terms Manometer