12.1 Characteristics of Gases & Pressure  Review: Gases are far apart from ea. other & do not tend to attract ea. other Are highly compressible Completely fill a container Have lower densities than solids/liquids (d = m/v)  Gases are considered to be fluids Fluid – when part’s can easily flow past ea. other  Gases have pressure Collisions bet. part’s & walls of container cause pressure Pressure = force / area SI Unit for pressure = Pascal (Pa) ○ 1 Pa = 1 N / 1m 2 Force = acceleration of object; SI unit = Newton (N)

 There are several units of pressure used  Meteorologists measure air pressure w/ a barometer  We can convert units of pressure UnitAbbrev.Conv. to Pa Atmosphereatm1 atm = 101,325 Pa Barbar1 bar = 100,025 Pa Millimeter of mercurymm Hg1mm Hg = Pa PascalPa1 Pounds per square inch psi1psi = x 10 3 Pa Torr 1 torr = Pa 760 torr = 760 mmHg = 1atm = kPa = 14.3 psi

 Kinetic-Molecular Theory Predicts gas behavior Gas part’s are in constant, rapid, random motion part’s are very far apart Pressure exerted by a gas is a result of collisions w/ part’s & the walls of a container Collisions are completely “elastic” – energy is completely transferred during collisions / total energy of system remains constant Gas temp is proportional to avg kinetic energy

12.2 The Gas Laws  Review: Pressure, vol, temp, moles  SI Unit for Temperature: Kelvin (K) K = ºC  Variables for gas laws: P = pressure exerted by gas T = temp in Kelvin V = total vol occupied by gas n = # moles of gas

 1662 Robert Boyle (English) studied the relationship bet. vol & press. As vol increased, press decreased & vice versa (inversely proportional) IF temp was constant Boyle’s Law– for a fixed amt of constant temp, the vol of the gas increases as press decreases & vice versa P 1 V 1 = P 2 V 2 ○ Units do not matter as long as same on both sides ○ Be careful! A problem may switch units on you so you will have to do a conversion 1 st

 1787 Jacques Charles (French) discovered that a gas’s vol is directly proportional to the temp on the Kelvin scale if press is constant Charles’s Law – for a fixed amt of gas at a constant pressure, the vol of a gas increases as temp increases and the vol of a gas decreases as temp decreases (balloon in flask lab!) V 1 V 2 T 1 = T 2 Remember, convert temp to Kelvin!!!

 1802 Joseph Gay-Lusaac (French) discovered that as temp increases, the avg. kinetic energy of a gas increases; therefore the press of a gas increases! Gay-Lusaac’s Law – the pressure of a a constant volume is directly proportional to the absolute temp (in Kelvin!) P 1 P 2 T 1 = T 2 Remember, convert temp to Kelvin!

 We can combine all 4 gas laws into 1 Combined Gas Law: P 1 V 1 P 2 V 2 T 1 = T 2

 1811 Amadeo Avogadro (your friend!) (Italian) developed the idea that equal volumes of constant temp & press will contain equal amounts of molecules – Avogadro’s Law This is how we discovered 22.4 L = 1 mole of any STP!!!

12.4 Avogadro’s Law  At constant temperature, volume is directly proportional to the number of moles of a sample of gas. V 1 V 2 n 1 = n 2

12.5 The Ideal Gas Law Molecular Composition of Gases  We need to assume that gases are ideal  Ideal gas – unlike real gases, doesn’t compress into a low temps, doesn’t have forces of attraction/repulsion, & is composed of part’s that have no volume  Ideal Gas Law room temp & atmospheric pressure, there is a mathematical relationship bet. press, vol, temp, a gas constant and n, the # of moles of a gas

The Ideal Gas Law Continued… PV = nRT R = L · kPa = L · atmmol · K

Gas Behaviors Diffusion – movement of particles from regions of high density to regions of low density (perfumes, etc) ○ Involves an increase in entropy (a measure of randomness) Effusion – passage of gas particles through a small opening ○ Why a tire w/ a nail goes flat ○ Why a balloon deflates over time