Chemistry Exam I 28 February 2018

Transcription

1 Chemisty - Exam I 8 Feuay 018 Name Show all wok o cedit. State any assumptions made to solve a polem. State all answes with the coect nume o signiicant igues. All answes in scientiic notation must e in pope scientiic notation (i.e., 6.0 not 6.0e o 6.0e). Each instance o impope scientiic notation will esult in the loss o thee () points. All numes equiing units must have the units included. Each instance o numes without units will esult in the loss o thee () points. 1. (8 pts) Ksp o silve chloide at 5.0 C is At 5.0 C, Ksp is Based on these data calculate H and S o the eaction. K1 H 1 1 ln = K R T T1 1 1 ( T T ) 1 K R ln J mol K ln K H = = = J mol RT ln K = H T S 1 1 ( ) K K H 1 1 S = Rln K + = ( J mol K ) ln ( 1.78 ) + T = 0.50 J mol K ( J mol K ) ( K)

2 . (4 pts) 0.0 ml each o enzene (C6H6) and toluene (C7H8) ae mixed togethe to make a solution. The density o enzene is g cm and it has a vapo pessue o 1.7 kpa at 5 C. The density o toluene is 0.87 g cm and it has a vapo pessue o.8 kpa at 5 C. What is the mole action o enzene in the vapo aove the solution in kpa? n t 1 cm g 1 mol 1 ml cm g = 0.0 ml = mol 1 cm t 0.87 g t 1 mol t 1 ml t cm t g t n = 0.0 ml t = mol t n = n + n = mol mol = mol x T t t n = n * * sol ' n t t, vap T mol = = mol x = 1 x = sol ' n sol ' n ( )( 1.7 kpa) P = xp + xp = kpa kpa = 8. kp x * P xp = = = = 0.84 P P 8. kpa

3 . (8 pts) An oxidation-eduction eaction occus etween the iodide ion and the chomate ion in asic solution. The alanced net ionic equation is: 5 HO + COØÈ + I C(OH) + IO + 4 OH a. Detemine i this eaction as witten is spontaneous at 15 C. Sustance (data at 5 C) ΔH (kj mol 1 ) ΔG (kj mol 1 ) S (J mol 1 K 1 ) Aqueous iodate ion Aqueous iodide ion Aqueous chomate ion Solid chomium(iii) hydoxide Liquid wate Aqueous hydoxide ion H = ν H ν H poducts eactants mol C OH 85.1 kj 1 mol IO 1. kj 4 mol OH 0.0 kj = + + mol xn mol C ( OH) mol xn mol IO mol xn mol OH = 99.1 kj mol 5 mol HO 85.8 kj mol CO kj 1 mol I kj + + mol xn mol HO mol xn mol CO4 mol xn mol I poducts 1 S νs νs = eactants mol C OH 1.4 J 1 mol IO J 4 mol OH.75 J = + + mol xn mol C ( OH ) K mol xn mol IO K mol xn mol OH K = 5 mol H O kj + mol xn mol HO K J mol K mol CO J 1 mol I 111. J + mol xn mol CO 4 K mol xn mol I K G = H T S = 99.1 J mol 88 K 9.1 J mol K = kj mol The eaction is not spontaneous at 15 C Detemine the equiliium constant o this eaction at 15 C J mol ( J mol K )( 88 K) 85 G K = e RT = e = 1.

4 4. (0 pts) Calculate the eezing point, oiling point and osmotic pessue, in a, o a solution that is made y dissolving g o ion(ii) acetate into g o wate at 0. C. The density o the solution is 1.1 g ml 1. Assume the van t Ho acto is the value expected om the chemical omula. ( ) g m ( ) ( ) ( ) 1.1 g sol'n 1 ml + 1 ml L 17.9 g Fe( C H O ) g Fe C H O 1 mol Fe C H O m= = g H O 1 kg 17.9 g Fe C H O g Fe C H O 1 mol Fe C H O M = ( g H O g Fe C H O ) = M ' ' 1 T = K mi = C m m =.0195 C T = T + T = C +.00 C =.00 C 1 T = K mi = 0.51 C m m = C mol 1 1 T = T + T = C C = 0.8 C π = imrt = L a mol K 9.5 K = 9.90 a L

5 5. (5 pts) Suppose you have availale.50 L o a solution (d = g/ml) that is 1.8% ethanol (CHCHOH), y mass. Fom this solution you would like to make the maximum quantity o ethanol-wate antieeze solution that will oe potection to.0 C. Would you add moe ethanol o moe wate to the solution? What mass o liquid would you add? Find molality o solution wanted: T =K m (.0 C) T m= = = m 1 K C m Find molality o the ethanol solution: 1.8 g CH5OH 1.8 g CH5OH g 1 mol CH5OH = = m 0.0 g sol'n 86. g solvent 1 kg g C H OH 5 The ethanol solution is moe concentated than it needs to e so we need to add wate: 1 ml g sol'n 1.8 g EtOH 1 mol EtOH.50 L sol'n = mol EtOH L 1 ml 0.0 g sol'n g EtOH mol EtOH 1.07 m = x kg wate x = kg wate = 6.8 kg wate total initial mass o wate is: 1 ml g sol'n 1.8 g EtOH 1 kg.50 L sol'n 1.47 kg wate = L 1 ml 0.0 g sol'n g mass needed is: 6.8 kg. kg = 4.7 kg wate to e added

6 6. (5 pts) Oxides o nitogen ae poduced in high-tempeatue comustion pocesses. The essential eaction is N + O NO. At what appoximate tempeatue will an equimola mixtue o N and O e 1.0% conveted to NO(g)? [Hint: Use data om elow as necessay.] Sustance (data at 5 C) ΔH (kj mol 1 ) ΔG (kj mol 1 ) S (J mol 1 K 1 ) N O NO N O NO N O ( 0.00) ( ) PNO K = = = 4.1 P P H = ν H ν H poducts eactants 4 mol NO 90.5 kj 1 mol N 0.00 kj 1 mol O 0.00 kj = mol xn mol NO + = kj mol mol xn mol N mol xn mol O S νs νs = poducts eactants mol NO 19.9 J 1 mol N J 1 mol O 05.1 J = mol xn mol NO K + = mol xn mol N K mol xn mol O K RT ln K = H T S ( ln ) H = RT ln K + T S = T S R K 1 H J mol T = = = K ( S Rln K) ( 4.1 J mol K ) ( J mol K ) ln ( 4.1 ) J mol K 1 1