2 Gas StoichiometryMany chemical reactions involve gases as a reactant or a productGas Stoichiometry – the procedure for calculating the volume of gases as products or reactantsGases have a molar volume (L/mole) rather than concentration.This is the conversion factor used to convert (litres of gas) to (moles of gas)The Ideal Gas Law (PV = nRT) may also be required to:A) find the number of moles of reactantB) Find the V, P, or T of the product
3 The conditions 0 0C and 1 atm are called standard temperature and pressure (STP). Experiments show that at STP, 1 mole of an ideal gas occupies L.PV = nRTR =PVnT=(1 atm)(22.414L)(1 mol)( K)R = L • atm / (mol • K)
4 PV = nRT nRT V = P 1.37 mole x 0.0821 x 273.15 K V = 1 atmo V = 30.6 L What is the volume (in liters) occupied by 49.8 g of HCl at STP?T = 0 0C = KP = atmoPV = nRTn = 49.8 g x1 mole HCl36.45 g HCl= 1.37 moleV =nRTPV =1 atmo1.37 mole x x KL•atmomol•KV = 30.6 L
5 PV = nRT n, V and R are constant P1 T1 P2 T2 = P2 = P1 x T2 T1 Argon is an inert gas used in lightbulbs to retard the vaporization of the filament. A certain lightbulb containing argon at 1.20 atmo and 18 oC is heated to 85 oC at constant volume. What is the final pressure of argon in the lightbulb (in atmo)?PV = nRTn, V and R are constantP1 = 1.20 atmT1 = 291 KP2 = ?T2 = 358 KP1T1P2T2=P2 = P1 xT2T1= 1.20 atmo x358 K291 K= 1.48 atmo
6 ExampleHydrogen gas is produced when sodium metal is added to water. What mass of sodium is necessary to produce 20.0L of hydrogen at STP?m? L2Na(s) H2O (l) 2NaOH(aq) + H2(g)20.0L x 1 mole = mole H2Lmole H2 x 2 mole Na = mole Na1 mole H2THEN mole Na x g Na = g Na1 mole= 41.0 g Na
7 ExampleIf the conditions are not STP, the molar volume cannot be used! You must use the ideal gas law to find the gas values using moles determined from stoichiometryWhat volume of ammonia at 450kPa and 80oC can be obtained from the complete reaction of 7.5kg of hydrogen with nitrogen?7500 g V ?2N2(g) H2(g) NH3(g)7500 g x 1 mole H2 = mole H2gmole H2 x 2 mole NH3 = mole NH33 mole H2Also: 450 kPa x 1 atmo = atmo and 80oC = KkPaPV = nRT V = nRTPV = ( mole)( Latmo/moleK)(353.15K)( atmo)= L x 104 L of NH3(g)
8 Gas Stoichiometry Summary Write a balanced chemical equation and list the measurements, unknown quantity symbol, and conversion factors for the measured and required substances.Convert the measured quantity to moles using the appropriate conversion factorCalculate the amount of moles of the required substance using the mole ratio from the balanced chemical equation.Convert the calculated moles to the final quantity requested using the appropriate conversion factor.
9 Gas StoichiometryBe careful! You CANNOT always use mole/ L
10 C6H12O6 (s) + 6O2 (g) 6CO2 (g) + 6H2O (l) Gas StoichiometryWhat is the volume of CO2 produced at 370 C and 1.00 atm when 5.60 g of glucose are used up in the reaction:C6H12O6 (s) + 6O2 (g) CO2 (g) + 6H2O (l)g C6H12O mole C6H12O mole CO V CO21 mole C6H12O6g C6H12O6x5.60 g C6H12O6= mole C6H12O66 mole CO21 mole C6H12O6mole x= mole CO20.187 mole x x KL•atmmol•K1.00 atm=nRTPV == 4.76 L
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