The Nature of Liquids Chp 10

The Nature of Liquids: Like gas particles, liquid particles are also in motion Unlike gas particles, liquid particles are attracted to each other

Intermolecular Forces: 1. Reduce the amount of space between liquid particles 2. Particles do not have sufficient amount of kinetic energy to overcome these forces 3. Therefore, they cannot escape to the gaseous state

Intermolecular Forces: Intermolecular forces are the reason why liquids are more dense than gases Liquid Gas

Evaporation: Conversion of a liquid to a gas or vapor, at the surface of the liquid Does not a require certain temperature or pressure How?

I have lots of kinetic energy H2O I can fly! H2O H2O H2O I do not have lots of kinetic energy

Evaporation: How? Some particles have enough energy to break away Some collide with air molecules and bounce back into the liquid

Evaporation and Heat: Increase the temperature = increase in averaged kinetic energy = increase in rate of evaporation

I’m not crazy your crazy Evaporation: Evaporation is a cooling process!! Particles with highest energy escape first! You must be crazy?? I’m not crazy your crazy

Evaporation: The liquids temperature decreases because there is a lower average kinetic energy of the particles left behind!!

You have probably experienced evaporation: Perspiration Water molecules absorb heat from your body and evaporate from your skin’s surface

Vapor Pressure: Evaporation of a liquid in a closed container Particles vaporize and collide with the walls of the container creating vapor pressure Vapor pressure = force due to the gas above the liquid

As time moves on, more particles vaporize Vapor Pressure: As time moves on, more particles vaporize Some will condense back into the liquid Eventually equilibrium will be reached between vapor & condensed particles

Vapor Pressure and Temperature: Increase in temp. = increase in vapor pressure Because of increased kinetic energy Particles are colliding with greater frequency

Manometer: Device used to measure vapor pressure Figure 10.9 illustrates a manometer

Boiling Point: The temperature at which the vapor pressure of the liquid is equal to the external pressure

If external pressure changes, the boiling point will change Example: Bell Jar experiment Lowered the pressure Water boiled at a lower temperature

Boiling Point: The higher the elevation = less pressure = the lower the boiling point There is less pressure pushing down on the liquid, therefore it is easier for the particles to escape! Water boils at 95o C in Denver

Boiling Point If we stood on the moon, we could boil water in our hands The atmospheric pressure on the moon is very low, therefore water boils at a much lower temperature

Look! I can boil Water in my hand

How does boiling differ from evaporation? How are they similar? Thought Questions: How does boiling differ from evaporation? How are they similar? Is boiling also a cooling process?

Now, go on to The Gaseous State Power Point Click Here to go on to The Gaseous State