OCTOBER 20OCTOBER 20

AIM: What is PRESSURE ?AIM: What is PRESSURE ?

Atmospheric pressureAtmospheric pressure

UnitsUnits

Gas pressureGas pressure

Air Pressure or Atmospheric pressureAir Pressure or Atmospheric pressure

Is the force that the atmosphere exerts Is the force that the atmosphere exerts over the surface of the Earth.over the surface of the Earth.

It depends on the weather.It depends on the weather. It changes with altitude.It changes with altitude. It is measured with a It is measured with a BAROMETER.BAROMETER.

Atmospheric pressure is the weight of air per unit of area.

Barometer

Evangelista Torricelli made the first barometer in 1644

UNITS FOR PRESSUREUNITS FOR PRESSURE

ATMOSPHERE = atmATMOSPHERE = atm Torricelli = torrTorricelli = torr Millimiters of Mercury = mm of HgMillimiters of Mercury = mm of Hg KiloPascal = kPaKiloPascal = kPa

Normal Atmospheric Pressure Normal Atmospheric Pressure (the pressure at sea level)(the pressure at sea level)

1 atm = 101.3 kPa = 1 atm = 101.3 kPa = 760 mm of Hg760 mm of Hg

STP - STANDARD TEMPERATURE AND PRESSURE

Table A

0 0 C or 273 K

1 atm=101.3 kPa=760 mm of Hg=760 torr

Gas pressureGas pressure

Gas particles are in continuous motion.Gas particles are in continuous motion. Gases exert pressure by colliding with Gases exert pressure by colliding with

the walls of the container they are in.the walls of the container they are in. The force exerted over the area of the The force exerted over the area of the

wall is the pressure of the gas. wall is the pressure of the gas. The greater the number of gas particles The greater the number of gas particles

in a container the greater the pressure.in a container the greater the pressure.

Collision against the walls of the container exert pressure

GasesGases

Have indefinite shape and indefinite Have indefinite shape and indefinite volume. Gases will assume the shape volume. Gases will assume the shape and volume of the container the are in.and volume of the container the are in.

The particles inside a gas are in constant The particles inside a gas are in constant motion.motion.

Gas particles exert pressure against the Gas particles exert pressure against the walls of the containerwalls of the container

October 21

BOYLE’S LAW

Relationship between pressure and volume for a gas

Boyle’s Law (1644)(1644)

The volume of a fixed quantity of gas at The volume of a fixed quantity of gas at constant temperature is inversely proportional constant temperature is inversely proportional to the pressure.to the pressure.

WHEN PRESSURE INCREASES THE VOLUME WHEN PRESSURE INCREASES THE VOLUME DECREASES (AT CONSTANT DECREASES (AT CONSTANT TEMPERATURE)TEMPERATURE)

As As PP and and VV are areinversely proportionalinversely proportional

A plot of A plot of VV versus versus PP results in a curve at results in a curve at constant Tconstant T

PV = k

EQUATION FOR BOYLE’S LAW PROBLEMS

P1 X V1 = P2 X V2 AT CONSTANT T

INITIAL FINAL

Review of Boyle’s Law problems Relationship between temperature and

volume of a gas at constant pressure- Charles’ Law

TEST ON GASES THURSDAY

OCTOBER 24

Jacques Charles-Charles’ Law - 1802

Charles’s Law

The volume of a fixed The volume of a fixed amount of gas at amount of gas at constant constant pressurepressure is directly is directly proportional to its proportional to its absoluteabsolute temperature. temperature.

A plot of V versus T will be a straight line.

VT

= k

EQUATION FOR CHARLES’ LAW PROBLEMS

T1 / V1 = T2 / V2 AT CONSTANT P

INITIAL FINAL

REMEMBER THAT TEMPERATURE MUST BE IN K

Problems with Charles’ Law

TEMPERATURE MUST BE IN K! Pressure is constant

OCTOBER 25

Review gas laws The combined gas law

THIRD LAW- RELATIONSHIP BETWEEN P AND T AT CONSTANT V

The pressure of a gas at constant volume is directly proportional to its K temperature

COMBINED GAS LAW

When no variable is kept constant.

OCTOBER 26

Kinetic Theory of Gases Ideal vs Real gases Deviation from ideal behavior TEST ON GASES TOMORROW

Kinetic theory of gases (under ideal circumstances)

Gas are composed of particles that are in constant, rapid, random, linear motion.

Collisions between gas particles are elastic so no energy is lost. As a result, the pressure of a gas at a constant temperature and volume remains constant

The volume of the particles of a gas is so small compared to the distance between them, it is considered zero. The gas is mostly space.

There is no attraction or repulsion between gas molecules

The average kinetic energy of the molecules of a gas is directly proportional to the Kelvin temperature of the gas

Deviation : noticeable or marked departure from accepted norms of behavior

Random : without definite aim, direction, rule, or method

Ideal Gas

Motion - at random Collision – cause pressure Volume – insignificant Attraction – no attractions

Deviations from ideal behavior

Particles of gas do have volume Gas particles do attract each other

Optimum conditions High temperature Low pressure Low molecular mass ( H2 and He are the lightest gases )

Real Gases

Motion - at random Collision – cause pressure Volume – can become significant Attraction –weak attraction- but do exist