Sample Problem 5.4Applying the Volume-Amount RelationshipPROBLEM:A scale model of a blimp rises when it is filled with helium to a volume of 55.0 dm3. When 1.10 mol of He is added to the blimp, the volume is 26.2 dm3. How many more grams of He must be added to make it rise? Assume constant Tand P.1M
5-30Sample Problem 5.4SOLUTION:n1= 1.10 molV1= 26.2 dm3n2= unknownV2= 55.0 dm3Tand Pare constantP1V1n1T1P2V2n2T2== 1.10 mol x55.0 dm326.2 dm3= 2.31 mol Hen2=V2V1n1xV1n1V2n2=Additional amount of He needed = 2.31 mol – 1.10 mol = 1.21 mol He1.21 mol He x4.003 g He1 mol He= 4.84 g He
Sample Problem 5.5Solving for an Unknown Gas Variable at Fixed ConditionsPROBLEM:A steel tank has a volume of 438 L and is filled with 0.885 kg of O2. Calculate the pressure of O2at 21oC.PLAN:We are given V, Tand mass, which can be converted to moles (n). Use the ideal gas law to find PV= 438 LT= 21°C = 294 Kn= 0.885 kg O2(convert to mol) Pis unknown.=g
Sample Problem 5.6Using Gas Laws to Determine a Balanced EquationPROBLEM:The piston-cylinders is depicted before and after a gaseous reaction that is carried out at constant pressure. The temperature is 150 K before the reaction and 300 K after the reaction. (Assume the cylinder is insulated.)Which of the following balanced equations describes the reaction?
5-33SOLUTION:PLAN:We are told that Pis constant for this system, and the depiction shows that Vdoes not change either. Since Tchanges, the volume could not remain the same unless the amount of gas in the system also changes.n1T1= n2T2Sample Problem 5.6Since Tdoubles, the total number of moles of gas must halve – i.e., the moles of product must be half the moles of reactant.This relationship is shown by equation (3).T1T2= n2n1= 150 K300 K= ½A(g) + B2(g) → AB2(g)