october 20 aim: what is pressure ? atmospheric pressure units gas pressure
TRANSCRIPT
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