T HE B EHAVIOR OF G ASES Unit 5 (part 2)

No definite shape No definite volume compressible P ROPERTIES OF G ASES (R EVIEW )

movingmoleculeswell supported ideas K INETIC M OLECULAR T HEORY

1) Gases consist of particles like atoms (ex: He) or molecules like (O 2 and CO 2 ) 2) There are no attractive forces. 3) Particles move in random, constant, straight-line motion. 4) Move independently of each other. 5) All collisions are elastic meaning that KE is transferred without loss of energy. B ASIC K INETIC T HEORY OF G ASES

- Gases tend to diffuse towards areas of lower concentration. D IFFUSION OF G ASES When 2 gases are mixed together

Pressure - force exerted on container walls by particles in a gas. Units used for pressure include: kPa (kiloPascals) or atm (atmospheres) STP (Standard Temperature and Pressure) Table A 273 K or 0°C and kPa or 1 atm GAS OR “VAPOR PRESSURE”

Amount of Gas (number of moles) Increasing amount will increase Pressure by overcrowding a container Ex: bicycle tires, car tires Temperature Increasing temp. will increase Pressure by speeding up particles Ex: Tires deflate in winter Volume Decreasing volume will increase Pressure by creating a tighter space Ex: press down on a balloon and it pops F ACTORS A FFECTING P RESSURE

Pressure and Volume have an inverse relationship, if temperature remains constant. If Volume is increased, Pressure is decreased by the same factor. P RESSURE VS. V OLUME Boyle’ Law P 1 V 1 = P 2 V 2

Volume and Temperature have a direct relationship, if pressure is held constant. If Temperature (in Kelvin) is increased, Volume is increased by the same factor. T EMPERATURE VS. V OLUME Charles’ Law V 1 /T 1 = V 2 /T 2

Pressure and Temperature have a direct relationship, if volume remains constant. If Temperature (in Kelvin) is increased, Pressure will be increased by the same factor. T EMPERATURE VS. P RESSURE G-Lussac’s Law P 1 /T 1 = P 2 /T 2

C OMBINED G AS L AW : *With all of these equations we can combine them to make the… * Found on Table T in reference table

USING COMBINED GAS LAW EQUATION Steps: Determine which variable is kept constant (if any) Remove the constants from the equation Plug in values that are given. Solve for the unknown.

1) If a student initially has 4.0 L of a gas at a pressure of 1.1 atm, how will the volume change if the pressure is increased to 3.4 atm? C OMBINED G AS L AW E XAMPLE 1: V 2 = 1.29 L

2) If a 10 L sample of nitrogen gas, initially at a temperature of 300 K is heated to 450 K at constant pressure of 1 atm, what would be the volume of the gas after heating? C OMBINED G AS L AW E XAMPLE 2: V 2 = 15 L

3) 2.0 L of a gas is examined at 25 °C and a pressure of 1.5 atm, what would the volume of this gas be at STP ? C OMBINED G AS L AW E XAMPLE 3: V 2 = 2.75 L

“Ideal gases” behave as predicted by Kinetic Molecular Theory. Gases are most ideal at high temperature and low pressure. I DEAL G AS VS. R EAL G AS : “Real gases” deviate from ideal behavior. At low temps, gas particles become attracted to each other (KMT says they are not). Under high pressure, gases occupy a specific volume (KMT says they don’t).

AVOGADRO’S LAW Avogadro’s number: 6.02 x The quantity of particles found in a mole. At STP, 6.02 x particles of a gas always occupy 22.4 L.

In a sealed container, vapor pressure can be measured above a liquid. Evaporation causes pressure to build up above the liquid VAPOR PRESSURE IN A CLOSED CONTAINER:

L IQUID -V APOR E QUILIBRIUM Some of the gas particles condense and then we find both evaporating and condensing occur at the same rate. Rate of Evaporation = Rate of Condensation

T ABLE H Notice, increasing temperature increases vapor pressure. Line drawn at kPa corresponds to normal boiling point. We use this table to find the new boiling point of a substance after a pressure change