Example Problem 30 L of H 2 at 20C are allowed to warm to a room temperature of

# Example problem 30 l of h 2 at 20c are allowed to

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Example Problem: 3.0 L of H2at –20°C are allowed to warm to a room temperature of 27°C. What is the volume then if the pressure remains constant? 2
Chem 1035 Chapter 5 24 of 46 3.0 L / 253 K = V 2 / 300 K V 2 = 3.6 L
Chem 1035 Chapter 5 25 of 46 Example Problem: A 20.0 L sample of NH3gas at 5.0°C has a pressure of 730 mmHg. What is the volume at 50°C and 800 mmHg? Example Problem: How many grams of O2gas are in a 50.0 L tank at 22°C if the pressure gauge reads 136 atm? How many O2molecules?
Chem 1035 Chapter 5 26 of 46 n = 281 mol O 2 281 mol O 2 * 32.0 g O 2 = 8,990 g O 2 281 mol O 2 * 6.022 x 10 23 molecules = 1.69 x 10 26 molecules O 2
Chem 1035 Chapter 5 27 of 46 The Ideal Gas Law and Gas Density Density = Mass / Volume PV = nRT Mass (g) / Molar Mass (g/mol) = moles = m PV = m / M (RT) P = mRT / MV P = dRT / M or d = PM/RT The density of a gas is Directly proportional to molar mass Directly proportional to pressure Inversely proportional to temperature Example Problem : Calculate the density of NH 3 at 752 mmHg and 55°C. 752 mmHg 1 atm = 0.989 atm 760 mmHg d = (.989 atm x 17 g/mol) / (0.0821 / 328 K) = 0.624 g/L
Chem 1035 Chapter 5 28 of 46 d = PM / RT T = 55 + 273 = 328 K
Chem 1035 Chapter 5 29 of 46 Gaseous Reactions Example Problem: If 50 g of Al is reacted with excess HCl according to the reaction below, what volume (in L) of H 2 will be produced at 700 mmHg and 30°C? LR XS 2Al( s ) + 6HCl( aq ) 2AlCl 3 ( s ) + 3H 2 ( g ) 50 g ? L Moles H 2 : 50 g Al. 1 mol Al 3 mol H 2 2.78 mol H 2 27.0 g. 2 mol Al PV = nRT 700 mmHg / 760 mmHg = 0.921 atm 0.921 (V) = (2.78) (0.0821) (303K) V = 75 L
Chem 1035 Chapter 5 30 of 46 Gas Mixtures Dalton's Law of Partial Pressures : In a mixture of gases, each gas exerts the same pressure it would if it were alone. The pressure of a mixture of gases is the sum of the partial pressures exerted by each gas: P total = P A + P B + P C + ….. Partial pressure: the pressure exerted by each individual gas in a mixture The pressure exerted by each gas is a function of the amount of each gas in the mixture: if moles go up, the pressure goes up Mole fraction:
Chem 1035 Chapter 5 31 of 46 X A = moles of gas A / total # of moles of all gases n A / n TOTAL
Chem 1035 Chapter 5 32 of 46 2
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