OCTOBER 20 AIM What is PRESSURE Atmospheric pressure

OCTOBER 20 AIM: What is PRESSURE ? Atmospheric pressure Units Gas pressure

Air Pressure or Atmospheric pressure l l Is the force that the atmosphere exerts over the surface of the Earth. It depends on the weather. It changes with altitude. It is measured with a BAROMETER.

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

Barometer Evangelista Torricelli made the first barometer in 1644

UNITS FOR PRESSURE l l ATMOSPHERE = atm Torricelli = torr Millimiters of Mercury = mm of Hg Kilo. Pascal = k. Pa

Normal Atmospheric Pressure (the pressure at sea level) l 1 atm = 101. 3 k. Pa = 760 mm of Hg

STP - STANDARD TEMPERATURE AND PRESSURE Table A 0 0 C or 273 K 1 atm=101. 3 k. Pa=760 mm of Hg=760 torr

Gas pressure l l Gas particles are in continuous motion. Gases exert pressure by colliding with the walls of the container they are in. The force exerted over the area of the wall is the pressure of the gas. The greater the number of gas particles in a container the greater the pressure.

Collision against the walls of the container exert pressure

Gases l l l Have indefinite shape and indefinite volume. Gases will assume the shape and volume of the container the are in. The particles inside a gas are in constant motion. Gas particles exert pressure against the walls of the container

October 21 l BOYLE’S LAW l Relationship between pressure and volume for a gas

Boyle’s Law (1644) The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure. WHEN PRESSURE INCREASES THE VOLUME DECREASES (AT CONSTANT TEMPERATURE)

As P and V are inversely proportional A plot of V versus P results in a curve at constant T PV = k

EQUATION FOR BOYLE’S LAW PROBLEMS l P 1 X V 1 = P 2 X V 2 INITIAL FINAL AT CONSTANT T

OCTOBER 24 l l l Review of Boyle’s Law problems Relationship between temperature and volume of a gas at constant pressure. Charles’ Law TEST ON GASES THURSDAY

Jacques Charles -Charles’ Law - 1802

Charles’s Law l The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature. V = k T A plot of V versus T will be a straight line.

EQUATION FOR CHARLES’ LAW PROBLEMS l T 1 / V 1 = T 2 / V 2 INITIAL AT CONSTANT P FINAL REMEMBER THAT TEMPERATURE MUST BE IN K

Problems with Charles’ Law l l TEMPERATURE MUST BE IN K! Pressure is constant

OCTOBER 25 l l Review gas laws The combined gas law

THIRD LAW- RELATIONSHIP BETWEEN P AND T AT CONSTANT V l The pressure of a gas at constant volume is directly proportional to its K temperature

COMBINED GAS LAW l When no variable is kept constant.

OCTOBER 26 l l Kinetic Theory of Gases Ideal vs Real gases Deviation from ideal behavior TEST ON GASES TOMORROW

Kinetic theory of gases (under ideal circumstances) l l l 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 l Random : without definite aim, direction, rule, or method

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

Deviations from ideal behavior l Particles of gas do have volume Gas particles do attract each other l Optimum conditions l l High temperature Low pressure Low molecular mass ( H 2 and He are the lightest gases )

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