 No definite shape ◦ It fills its container  Compressible ◦ With increases in pressure  Low Density ◦ Molecules are far apart ◦ Intermolecular forces are ignored  Diffusion ◦ Molecules can randomly spread out

 Theoretical description of gases ◦ Disregard the volume of the molecule itself ◦ Disregard any attractive force between molecules  Real gases stray from ideal gases at: ◦ LOW Temperatures ◦ HIGH Pressures

 At STP (Standard temperature and pressure), all gases have a volume of 22.4 L.  Standard Temperature: ◦0oC◦0oC ◦ 273 K  Standard Pressure: ◦ kPa ◦ 1 atm ◦ 760 torr (or mmHg)

 The volume of a quantity of gas, at constant pressure, varies directly with the Kelvin temperature.  Temperature MUST be in Kelvin! ( o C + constant Pressure

 A gas is collected at 58 o C and has a volume of 225mL. What volume will it occupy at standard temperature, if pressure remains constant?

Since the temperature decreases, pressure must decrease! T 1 = 331 K V 1 = 225 mL T 2 = 273 K V 2 = ? 186 mL = L

 As pressure increases, volume decreases.  Temperature MUST be constant.

 A sample of O 2 gas at 0.947atm has a volume of 150mL. What would its volume be at 0.987atm if the temperature stay constant?

P 1 = atm V 1 = 150 mL P 2 = atm V 2 = ? 144mL = 0.144L

Volume is constant * Remember, Temperature MUST be in Kelvin

 An aerosol can has a pressure of 103 kPa at 25 o C. It is thrown into a fire and its temperature increases to 928 o C. What will its pressure be?

P 1 = 103 kPa P 2 = ? T 1 = 25 o C = 298 K T 2 = 928 o C = 1201 K P 2 = 415 kPa

 The volume of a gas-filled balloon is 30.0 L at 313 K and 153 kPa. What would the volume be at STP?

V 1 = 30.0L T 1 = 313 K P 1 = 153 kPa V 2 = ? T 2 = 273 K P 2 = kPa V 2 = 39.6 L

P = pressure V = volume (in Liters!) n = moles T = temperatre (in Kelvin!) R = gas constant Gas constants

 What volume would be occupied by 1.00 moles of gas at 0 o C at 1 atm pressure?

P = 1 atm V = ? n = 1 mol R = (because pressure is in atm) T = 0 o C = 273 K V = 22.4L

 Equal volumes of gases at the same temperature and pressure contain equal numbers of particles.  Molar Volume- for a gas, the volume that one mole occupies at STP ◦ Temp = 0 o C or 273K ◦ Pressure = 1 atm or kPa or 760 torr (mmHg) 1 mole = 22.4 Liters

 Determine the volume of a container that holds 2.4 mol of gas at STP.

54 L

 If 100L of hydrogen gas react at STP, how many grams of hydrogen chloride can form?

326 g HCl

 The sum of the individual gas pressures equals the overall pressure of the mixture of gases.

 If a container has 166 torr H 2, 109 torr CO 2 and 176 torr of O 2, what is the total pressure of the mixture? 116 torr torr torr = 401 torr

 Our atmosphere is made of 21% O 2, 78% N 2 and 1% other gases. At sea level (standard pressure), what is the partial pressure of oxygen? 760 torr x 0.21 = 159 torr O 2

 The spontaneous spreading of particles  The rate of diffusion depends on the velocities and masses of the molecules  Effusion – the process by which a gas escapes from a small hole in a container  Lighter gases ALWAYS diffuse/effuse faster than heavier molecules

 The relative rates at which two gases, at the same temperature and pressure, will diffuse, vary inversely as the square root of the molecular mass of the gases. **Always consider gas 1 the lighter gas

 Compute the relative rates of diffusion of helium and argon. ◦ go to the periodic table for molar mass of He and Ar

Mass He = 4 g/mol Mass Ar = 40 g/mol So, helium diffuses 3x’s faster than argon.