More with Equilibrium In a closed container phase changes occur until an equilibrium is reached

Liquid to Gas In a closed system at a constant temperature… Molecules at the surface have enough kinetic energy to vaporize…the intermolecular forces are broken. The vapor molecules collide with surface molecules…slower moving molecules condense. When the rate of condensation = rate of vaporization an equilibrium is reached The pressure is constant…changing the pressure will change the equilibrium

The pressure exerted by vapor at equilibrium is known as equilibrium vapor pressure or vapor pressure. Decrease the pressure—the volume increases the rate of condensation is less than rate of vaporization Increase pressure the volume decreases so the rate of condensation is greater than the rate of vaporization

The effects of temperature and intermolecular forces on vapor pressure. An increase in temperature allows the molecules to move faster which allows for a higher vapor pressure—weaker intermolecular forces.

The boiling point of a liquid is when the vapor pressure is = to the external pressure (usually 1 atm). So boiling depends on applied pressure. Boulder Colorado water boils at 940C Pressure cooker increases the pressure so the boiling point is increased –cooks faster

Solid - liquid Crystal particles vibrate eventually breaking free as temperature increases-melting begins Some liquid (molten) molecules collide with solid becoming fixed again Equilibrium is when melting rate = freezing rate Temperature remains constant until all of the substance is melted-pressure has no effect (can’t easily compress liquids and solids)