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13.2 The Nature of Liquids. Describe the particles in a liquid. 13.2 The Nature of Liquids Liquid particles are attracted to each other The particles in a gas are not. Intermolecular Forces. Dipole-Dipole Dispersion Hydrogen Bonds. Dipole – Dipole Forces. London Dispersion Forces.
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13.2 The Nature of Liquids • Liquid particles are attracted to each other • The particles in a gas are not
Intermolecular Forces • Dipole-Dipole • Dispersion • Hydrogen Bonds
Particles of a liquid spin and vibrate while they move, adding to their average kinetic energy • Most of the particles do not have enough energy to escape into the gaseous state; must overcome their intermolecular attractions
The intermolecular attractions reducethe amount of space between particles of a liquid • Liquids are moredense thangases • Increasing pressure on liquid has hardly any effect on it’s volume
Vaporization -the conversion of a liquid to a gas or vapor • Evaporation -when this occurs at the surface of a liquid that is not boiling • Some of the particles break away and enter the gas or vapor state; but only those with certain minimum kinetic energy escape from the surface of the liquid
Why does a liquid evaporate faster when heated? • Explain how evaporationis a cooling process • What about the particles left behind?
Evaporation of a liquid in a closed container • Fig. 13.6b on page 391 shows that no particles can escape into the outside air • When some particles do vaporize, these collide with the walls of the container producing vapor pressure
A measure of the force exerted by a gas above a liquid is called the vapor pressure.
Dynamic equilibrium • Rate of evaporation = rate of condensation
An increase in temperature of a contained liquid increases the vapor pressure • the particles have an increased kinetic energy, and more minimum energy to escape
Boiling Point (bp) • The temperature at which the vapor pressure of the liquid is just equal to the external pressure on the liquid
Since the boiling point is where the vapor pressure equals external pressure, the bp changes if the external pressure changes • Normal boiling point- the bp of a liquid at a pressure of 101.3 kPa (or standard pressure)
Water boils at 100° C • in Denver = ? • Denver is 1600 m above sea level and average atmospheric pressure is about 85.3 kPa