13.2 The Nature of Liquids

Describe the particles in a liquid

Liquid particles are attracted to each other 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

Hydrogen Bonding

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 reduce the amount of space between particles of a liquid Liquids are more dense than gases 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 evaporation is 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