Key Chemisry 0 Discssion #4, Chaper and Sden name TA name Secion. Two idenical conainers, one red and one yellow, are inflaed wih differen gases a he same volme and pressre. Boh conainers have an idenically sized hole ha allows he gas o leak o. I akes for imes as long for he yellow conainer o leak o compared o he red conainer. If he red conainer is wice as ho as he yellow conainer, wha is he raio of he molar masses of he gases ( yellow / red). rae rae Rae(R) Rae(Y) = Y ; (Y) = 4 R = T(Y) (R) T(R) 3RT ; = 3RT and T(red)=*T(yellow) ; (yellow)=4*(red) or Rae(R)=4Rae(Y) (Y) T(R) T(Y) = = (Y) = (Y) (R) T(Y) (R) T(Y) (R) = (Y) (R) = 6 (Y) (R) = 8. A conainer is filled wih He a 8 o C and 7.9 bar. I is fond ha he pressre of he conainer drops by 50% in 35 mines, de o a small hole. If he conainer had insead been filled wih Ne a 8 o C and 7.9 bar, wha wold be he pressre of he Ne afer 35 mines? Express yor answer in bar. a. He =0.50*7.9bar=3.96 drops by 50% = f in=3.96 7.9= -3.96 ; rae [amon] b. ; Rae= rae ime c. raehe raene He He Ne =.46 Ne Ne He d. Ne = He He =.76 or.6% ; Ne Ne = -.76 becase pressre of he conainer drops e. Ne= in + =(7.9+(.76))bar=6.6bar n V 3. Solve he van der Waals real gas eqaion a V bn nrt V nrt bn conainer n a V con an er, for he pressre. a. To invesigae how he a coefficien affecs he pressre, se he b coefficien o zero. Does a increase or decrease he pressre compared o wha yo wold expec for an ideal gas? nrt n a V V a <ideal a is responsible for lowering he pressre conainer Sronger he inermoleclar forces greaer he vale of a.
V/RT b. To invesigae how he b coefficien affecs he pressre, se he a coefficien o zero. Does b increase or decrease he pressre compared o wha yo wold expec for an ideal gas? nrt b >ideal a is responsible for increasing he pressre Vconainer bn Bigger he volme of he molecles he greaer he vale of b c. Below is a plo of he compressibiliy (V/RT) as a fncion of changing pressre for mole of a real gas (dashed line) and an ideal gas (solid line). Using wha yo learned in pars (a) and (b), a wha pressres is he a coefficien dominan and a wha pressres is he b coefficien dominan. ( y axis is (V/RT)real / (V/RT)ideal).75.5.5 0.75 0.5 0.5 0 ressre vs. Compressibiliy of van der Waals gases 0 00 00 300 400 500 ressre (am) a dominaes a low pressres and b dominaes a high pressres 4. he following molecles in increasing order of van der Waals consan, b? Cl, N, CH6, C3H8. N, <Cl, <CH6, < C3H8, Bigger he volme of he molecles he greaer he vale of b 5. For each of he pair of molecles below, which has he highes vale of van der Waals consan, a? Idenify he dominan inermoleclar forces. HO vs CO Ne vs F,
C6H6 vs CH3OH 6. Which of he following gases will behave leas ideally nder he same condiions? Explain yor choice sing he a and b van der Waals coefficiens. ( he molecles wih greaes volme and sronger Inermoleclar forces) CH4 or SO Cl or N 7. ach he molecles below wih heir a and b van der Waals coefficiens. (Hin: Look a he vale of b firs and decide based on he size of he molecles and hen hink abo Inermoleclar forces ) Gas a (L am mol - ) / b (L mol - ) Waer (HO) 0.476 / 0.066 Argon (Ar) 5.536 / 0.0309 Hydrogen (H).363 / 0.039 Benzene (C6H6) 8.4 / 0.54 8. O and HO have similar vales of van der Waals consan, b, b differen van der Waals consan, a which one will have higher pressre a he same emperare and volme. (HO) < (O) a <ideal a is responsible for lowering he pressre Sronger he inermoleclar forces greaer he vale of a. 9. NO and Trifloromehane (CF3H) have similar vales of Van der Waals consan, a, b differen van der Waals consan, b which one will have higher pressre a he same emperare and volme. (NO) < (CF3H) b >ideal a is responsible for increasing he pressre Bigger he volme of he molecles he greaer he vale of b 0. ( A home ) A 5.0mol sample of NH3 gas is kep a.0 L conainer and 7 C, Calclae he pressre in bars of he gas assming i does no behave ideally. (a=4.0 bar L /mol and b= 0.040L/mol) V nrt bn conainer n a V 5.0mol 0.0834 (L bar)/(mol K) 300.5K =.0L 0.040(L/mol) 5.0mol 4.0 (bar L /mol 5.0mol ).0L =44.379bar ideal= nrt =6.386 V conainer Wha is he percen error compared o an ideal gas? % error= 00% * ( - ideal) /ideal 3
. Consider a balloon filled wih 5 N gas and placed in larger conainer filled only wih 4 N. If a small hole is made in he balloon, iniially as he gases effse, will he balloon expand, conrac or say he same volme? Assme he pressres inside he balloon and in he conainer are he same. Explain yor answer. I may help o draw a picre. Increase 4 N 5 N. Two idenical conainers, one red and one yellow, are filled wih differen noble gases a he same emperare and pressre. Boh conainers have an idenically sized hole in hem allowing he gases o leak o. If i akes he red conainer 0.0 seconds o empy and he yellow conainer 57.3 seconds o empy, wha are he noble gases conained in each conainer? ( Remember: rae is proporional o /ime) rae ; rae 3RT ; T(red)=T(yellow) Rae(Red) = = ; red= 3RT ime(red) 0 ( red) Rae(yellow) = ime(yellow) = RaeR RaeY = ( 0 ) ; yellow= 3RT 57.3 ( yellow ) ( 57. 3 ) = 57. 3 0 = (red) (yellow) = Y R Y (Xe) R (He) = (5. 73) = 3. 8 (exac) ~ 5 36 (depends on ronding) He: 4 * 30 = 0 (Xe) 3. In.00 min, 9.7mL of helim effses hrogh a small hole. Under he same condiions (emperare and pressre), a 0.00 ml of a mixre of CO and CO effse hrogh he same hole in he same amon of ime. Calclae he percen composiion by volme of he mixre. V=nRT ; V= nrt mix He V ; rae ~ ime = rae(he) rae(mix) = 9. 7mL. 00 min =. 9 0. 00 ml. 00 min (mix) = (. 97) 4 g = 35. 3 g/mol mol χco + χco = χco *(8g/mol) + χco*(44 g/mol) = 35.3 g/mol χco = 45.5% χco = 54.5% 4
4. Two idenical conainers are filled wih he same nmber of moles of gas a he same emperare. Conainer A conains a gas wih a molar mass of 40. g/mol, and conainer B conains a gas wih a molar mass of 60. g/mol. A hole of idenical size is hen made in each conainer. Wha is he raio ime A/ime B of he imes necessary for he nmber of moles of gas o drop o half in each conainer? RaeB RaeA = a b = a b = 0. 5 5. Imagine a sbsance wih he following poins on he phase diagram: a riple poin a.5 am and -5 C; a normal meling poin a 0 C; a normal boiling poin a 50 C; and a criical poin a 5 am and 000 C. For his, complee he following: a. Wha does i mean o have a normal solid-liqid line? b. Roghly skech he phase diagram, sing nis of amosphere and T C. ressre (am) 5-80 -5 0 50 500 000 0 Temperare ( C) a. Rank he saes wih respec o increasing densiy: s > l > g b. Describe wha one wold see a pressres and emperares above 5 am and 000 C. spercriical flid separaion beween liqid and gas disappears. c. Describe wha will happen o he sbsance when i begins in a vacm a -5 C and is slowly pressrized. g s d. Describe he phase changes from -80 C o 500 C a am. S L g 5
6. For each of he following qesions refer o he phase diagram for myserios compond X. If yo were o have a bole conaining compond X in yor close, wha phase wold i mos likely be in? above 750ºC 3) A wha emperare and pressre will all hree phases coexis? 50 am; 350 ºC 4) If I have a bole of compond X a a pressre of 45 am and emperare of 00ºC, wha will happen if I raise he emperare o 400 C? s g sblimaion 5) Why can compond X be boiled a a emperare of 00 C? No, becase liqid phase is a 00ºC 6) If I waned o, cold I drink compond X? NO 6