7-4 Avogadro’s Principle (Section 13.4 ) And you!

Avogadro’s Principle states that for a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas. In equation form: Volume = constant x moles or V = constant x n

Rearranging gives us: V1 = constant = V2 or V1 = V2 n1 n2 n1 n2 Another way to interpret this principle is: equal volumes of different gases (at constant T and P) have the same number of molecules.  

7-5 The Ideal Gas Law (Section 13.5) It’s possible to combine all the gas laws we’ve learned into one expression called the Ideal Gas Law: PV = nRT P = pressure V = volume (in L) (= 22.4L @ STP) n = number of mole T = temperature (in K) R = the Universal Gas Constant = 0.08206 L•atm = 8.31 L•kPa = 62.4 L•mmHg mol•K mol•K mol•K All the gas laws can be derived from the Ideal Gas Law; for example, by holding V and n constant.

The Ideal Gas Law can be used to calculate additional quantities other than P, V, and T: Using the idea that the molar mass (formula weight) = grams/mole or MM = grams/n Therefore: n = g/mm Sub in for n gives: PV = g •RT MM so MM = gRT/PV !!!!! Used to identify the type of gas you have based on the calculated MM and the periodic table values!!!!

Rearrange for Density: d = g/ml so d = g/V MM = g RT so g/V = mm/ (RT/P) V P Density of gas = (g/V) = P(MM) / RT

Last section of notes 7-5 At STP T = 273K and P = 1 atm PV = nRT so V = nRT/P If n = 1 mole: V = 1(.0821)(273)/1 = 22.4L So 36 g H2O (1 mol/18.02g) = 2 moles H2O V = 2 (.0821)(273) / 1 = 44.8 L