Chapter 13States of Matter

Section 13.1: Nature of Gases

• Kinetic Theory and a Model for Gases

– Kinetic Energy: Energy that an object has because of its motion

– Kinetic Theory: All matter consists of tiny particles that are in constant motion

• Particles in a gas are usually atoms/molecules.

• There are three fundamentals to the kinetic theory applying to gases which we will review one by one.

Kinetic Theory: Fundamental # 1

• Particles in a gas are considered to be small, hard spheres w/ insignificant volume.

- a lot of empty space between particles

- no attractive/repulsive forces b/w

particles

- Motion of 1 particle is independent

from the motion of other particles

Kinetic Theory: Fundamental #2

• Motion of particles in a gas is rapid, constant and random

- a gas will fill the shape of any container

- uncontained gas spreads out with no limit

- gas particles will travel in a straight path until they collide with something else

Why would individuals in Mexico not be able to smell pizza from a shop in Washington D.C? (Oxygen molecules can travel 1700 km/h at 20 degrees Celsius)

Kinetic Theory: Fundamental # 3

• All Collisions between particles in a gas are perfectly elastic

Elastic Collision

-Total kinetic energy remains constant between 2 molecules.

-No K.E. is lost, only transferred

Example:

Observe and record how Newton’s cradle works.

Gas Pressure– Gas Pressure: result of simultaneous collisions of billions

of rapidly moving particles in a gas with an object.

– In a vacuum, there is no pressure. Why?

• Demonstration: Marshmallow peep in a vacuum

Layers of the Atmosphere

Components of Dry Troposphere AirSubstance Formula Percent of All

Gas MoleculesMajor ComponentsNitrogen and Oxygen

N2 O2

78%21%

Minor ComponentsArgon Carbon Dioxide

Ar CO2

.93%

.033%

Trace Amounts Ne NH3

He CH4

.0018%

.0010%

.0005%

.0002%

Atmospheric Pressure• What is atmospheric pressure?

•Results from the collisions of atoms and molecules in air with objects

•Air exerts pressure on earth b/c gravity holds particles in the atmosphere.

As you climb higher up a mountain, does atmospheric pressure increase or decrease? Why?

Atmospheric Pressure• How much pressure are you under? Earth's

atmosphere is pressing against each square inch of you with a force of 1 kilogram per square centimeter (14.7 pounds per square inch). The force on 1,000 square centimeters (a little larger than a square foot) is about a ton!

• Why doesn't all that pressure squash me?

Remember that you have air inside your body too, that air balances out the pressure outside so you stay nice and firm and not squishy.

Atmospheric PressureWhy do my ears pop?• . As the number of molecules of air around you decreases, the

air pressure decreases. This causes your ears to pop in order to balance the pressure between the outside and inside of your ear.

• Why do athletes and trainers often recommend high altitude training as a means to increase exercise endurance?

At higher altitudes, less oxygen results in the heart working harder.

Measuring PressureBarometer: used to measure

atmospheric pressureThe SI units of pressure is Pascal (Pa)

other units: Millimeters of Mercury (mm Hg)

atmospheres (atm

1 atm = 760 mm Hg = 103.3 kPa

Old Mercury Barometer Is Shown to the Left.

Low pressure = Bad Weather

FF High pressure = Good Weather

Converting between Units of PressureSTP = ( 101.3kPa or 1 atm)

Example 1) A pressure gauge records a pressure of 450 kPa. What is the measurement expressed in atmospheres and millimeters of mercury?

Outer SpaceHW: Consider the following…

What would happen if you were in outer space without a space suit?

-Think about…

-atmospheric pressure

-temperature

-gravity

Kinetic Energy and Temperature

• What’s the difference between Heat and Temperature?

• Heat = Energy• Temperature = measurement of heat

• When a substance is heated, its particles absorb energy- some is stored as P.E.

• The rest of the energy speeds up the particles and increases K.E.

•The faster the particles move, the higher the temperature!

Average Kinetic EnergyAt a given temperature, the kinetic

energy for different types of atoms/molecules is averaged.

Kelvin temperature is directly proportional to avg K.E of particles in a substance.

Ex) Helium gas.

200 K K.E. = 2x

100 K K.E. = x

Kinetic TheoryIs it possible for particles to have absolutely no motion?

Absolute Zero is the temperature at which the motion of particles theoretically ceases. (-273.15 degrees C)

Absolute Zero has never been produced in a laboratory

Section 13.2 The Nature of Liquids• Liquids, like gases

– can fill the shape of a container because liquid particles have K.E.

– Can flow

• Unlike gases, particles in a liquid are – held together by stronger

intermolecular forces.– Closer together and more dense

Evaporation• Vaporization: conversion of a liquid to a gas/vapor

• When such a conversion occurs at the surface of a liquid that is not boiling, the process is called evaporation

During evaporation…

-only molecules with enough KE can overcome the intermolecular forces between the molecules and escape from the surface of a liquid

When a liquid is heated…• heat adds KE to particles

• added energy allows particles to overcome intermolecular forces

• Molecules with highest KE escape liquid

• Remaining molecules have lower KE

• What happens to the temperature of your body when you sweat?

• As evaporation occurs, temp decreases• Evaporation is a cooling process

Vapor PressureVapor refers to a gas phase at a temperature where the same

substance can also exist in the liquid or solid state

Vapor Pressure: is a measure of the force exerted by a gas above a liquid

Vapor Pressure + Temp ChangeIncreased Temp of contained Liquid = Increased Vapor Pressure

When temp increases, more particles vaporize and create greater pressure from colliding with each other and the container.

Manometer: measures the vapor pressure of a liquid

You determine the vapor pressure in mm Hg by measuring the difference between the two levels of mercury.