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CHEM HOUR EXAM II 1021 10/25/00 THIS IS VERSION A DON'T FORGET TO ENCODE YOUR NAME, ID#, AND EXAM VERSION (A,B, or C) ON THE BUBBLE SHEET PROVIDED. BE SURE TO USE #2 PENCILS ONL y THE RANDOM ID# APPEARING ON YOUR BUBBLE SHEET WILL BE USED FOR THE PURPOSE OF POSTING YOUR SCORE. PLEASE BE SURE TO RECORD IT IN THE BOX BELOW. YOU SHOULD KEEP YOUR EXAM. GOOD LUCK! Random ID# = KEY A Pleaseindicate the correct answer for each question. Each question is worth 5 points. There is only one correct answer per question. Questions with more than one answer will receive no credit. No partial credit will be given. Scratchwork doesn't count, right or wrong! No answers given in the blue books will be counted. Some Possib~v Us~{ul 11?{ormation: Partial Pressure: Mole Fraction: PT = PJ + P2 + PJ+ Universal Gas Constant: 0.08206 atm 1/mo1/K 8.314 J/mol/K Ideal (7)1/2 Graham's Law (Rate r)/(Rate2)= (M2/ Ml)I/2 LlE=q+w Expans i on/ Corn pres si on Work (Against Constant P): w = -PL\V Enthalpy: H=E+PV Heat: q=smL\T Light: c= E= A= Ay c= 3.00x108 mls hy h= 6.626x h/mv me= 9.11x10-31 kg Kinetic Theory: First Law of Xi = nj/nT = Pj/PT = (3RT/M)1/2 Thermodynamics DeBroglie wavelength: NOTE: A PERIODIC TABLE IS ATTACHED Molar Volume @ STP 1 atm = 760.00 torr Gas Law: 22.4 liters PV = nRT TO THE BACK OF THIS EXAM. 10-34 J s '!. \"S ,L 1 A sample ofhelium~ will (a) (b) c!f;p (e) it occupy 1"2,q (, \l. occupies 12.41iters at 40. °C and 1.20 atm? 11 V, v\--:~ liters -1'<. T, 0.488 6.28 liters 12.4 liters 10.4 liters 17.2 liters at 2:r:C ; (I. (2. T 1.. v")..: I ' lo ~ = 10.4 2. A gas mixture and 0.956 atm. What volume c~ -{ is prepared by mixing 1.0 moles of gas A, 2.0 moles orgas B, and 3.0 moles ofgas C. The final pressure is 15 atm. What is the partial pressure of gas B? ? ' 0., o ) ~ -1.0 +-i,~+ 310) (a) 2.0 atm \1 = "';i'1? :; ~ ~ 'lC5 (d) (e) 3 5.0 6.0 7.0 10. atm atm atm atm .=-- 01 $ 33 Yl\'3; - )'1.,... 'P-r =., ?=t?= Which of the following is not an assumption of the kinetic theory of gases? ~ (b) ( c) (d) (e) The average velocity of the gas particles is directly proportional to the pressure. Gas particles are very small compared with the average distance between particlesGas particles collide with the walls of their container and in doing so give rise to pressure. Gasesare made up of tiny particles in constant, chaotic motion. Gas particles do not interact with one another. 4. Gaseous C2~ reacts with O2 according to the following equation: C2H4(g) + 302(g) ~ 2CO2(g) + 2H2O(g) What volume of oxygen at STP is needed to react with 1.50 mol of C2H4? l '\ '3~((. ~~ I , .«;.'-0 ~0\( C1..1-1'1 I ~ -Lf.~-o Mo (a) 4.50 liters , htr>f~ Ca./~1I (b) 33.6 liters "2. "2 I 4 ...e ><..Q (1£D 10lliters =? )( .: .AT ~TP ( d) 67.2 liters 4 ' l'"() ('lA 0 , I.()O rn,1 (e) 85.0 liters 5 /" "'-'1... 10 I ..1<. Which of the following gases would have a higher rate of diffusion than C2H2 under the same conditions of temperature and.RJltessure? II ~. r')1"br fVI,4t ,f " N2~1.~ IJuLl..ol..,1e .1 ; 24+1..:2.' (a) (b)I a2 C12 ~ Cll4 ~ CO2 ~ ~ ~ "1 f v\olola. ,.. I)oItA' l' ~~\. ~ , I (.-. -/...IL-l A sample ofN2 gas is mixed with a gas (A) of unknown molar mass. The partial pressures of each gas are known to be 200. torr. The gases are allowed to effuse through a pinhole and itofisAfound that gas A escapesat three times, tl.Ie rate of N2. What is the molar mass ? 6. 1 (1;1) (b) (c) (d) (e) 3.11 252 84.0 9.33 2.00 \~1S R~ .: -, - 3p == --(\I\ ('FJ~ ) )(. ::~ ~<A) I1Atc.. u~ 9,0 t 'C'",I...J - '::- ~ ~ )( : 3, ~ At 100QoC, and a pressure of 10. Torr, the density of a certain element in the gaseous state is 2.9 x 10-3 g/liter. What is the element? (Remember that there is a periodic table at the end of the exam. Also, please be careful with your units.) 7, ~= (a) cf? (e) d."li- Ne He Na Ar Hg (tIt 1tA.=- ~ =-~ p ~ (i ~ "2~ d l().td 0 ftot-r ). Consider the two samples of gas shown below: 8. 0 I~ Sample A Sample T = 300 K p = 1 atm 2 Cc-~ B T = 300 K p = 2 atm V= 1.01iter V= 1.01iter Which of the following statementsis true? J:ar J:br There are more atoms in Sample A than in Sample B. Ja~;~rl The argon atoms in Sample B have, on average, more kinetic energy than I the xenon atoms in sample A. The density of Sample A equals the density of Sample B. The number of moles is the same in both samples. Xenon atoms in Sample A are moving, on average, slower than the argon atoms in Sample B. ~ I :--"'\'/l..=I'i"PT I .,1J " Ii( -"'\...u..'). ) , ~ J /V\~ ~ ,4 ~ W@ 9. Consider the following properties of a substance: \£. I. mass V II. i III. temperature volume v IV. concentration "" V. energy (moles/liter) Which of these is(are) intensive? (a) @ (d) (e) 10. I, III, and V only II only II and IV only III and IV only I and V only Calculate the change in energy associated with the expansion of a gas from 152 liters to 189 liters against a constant pressure of 14 atm. Assume that no heat is exchanged in the process, and be sure to apply the same sign convention we adopted in class. ~ r/° i') .1 b.Eh+\..(J =-\Dv 520 liter atm (a) I~Cf~ -/,.s-2-R. ) : -520 liter atm @1) = -( I ~ ~~ ) -260 liter atm (c) 175 liter atm (d) .: -( ty ~~ ) 260 liter atm (e) Which of the following will cause py to be less than nRT for a real (non-ideal) gas? 11. (a) (b) Some molecules in the sample have speedsless than the average speed. Some molecules in the sample have speedsgreater than the average speed. The gas molecules have a very low molecular mass. The gas molecules attract one another. None of these. Which of the following statementsabout ozone is incorrect? 12. (a) (b) CW (e) The chemical fomlula of ozone is 03. Ozone can be found as a trace gas in both the stratosphere and in a polluted troposphere. Ozone is an important greenhousegas in the troposphere. The ozone layer is found in the stratosphere. Ozone participates in the fomlation of photochemical smog. Consider the reaction 13 C2HsOH(I) + 302(g) ~ 2CO2(g) + 3H20(1) For the reaction as written, ~H = -1370 kJ. When a 15.1 9 sample of C2HsOH is burned at constant pressure, how much energy is released as heat? The molar mass of C2HsOH is 46.1 g/mol. ~ 1.5"".lq I.J.W (b) (c) (d) (e) 449 2250 0.449 1020 196 kJ )( o kJ kJ kJ kJ ~~\(. ~ Mf>( 4 ' ( ~ J=- o.$2i' ()?u .12 C').I.JrC:>H ~ lJ'1o1 I c1.I.JroH ==- \ s 70 t.(. :r ~ '}( = 4 L-/q 1<:4" For a particular 14. process, q = 20 kJ and w = 15 kJ. Which of the following statements is(are) true? ~ UJ ~ Heat flows from the system to the surroundings. The system does work on the surroundings. L\E = 35 kJ ~ (e) All of the above are true. None of the above are true.() b rh \.Y-1 £ :::-7 +- L<) : '3 s- I<.T 5 Given the following thernlochemical data: H20(1) ~Ho ---,-f -286 HC1(g) -92 kJ/mol Substance kJ/mol Calculate the standard enthalpy change, ~Ho, for the reaction CI2(g) + H20(1) ~ 2HCl(g) + (1/2)02(g) O -2~' -,').. 0 102. (£L (@1::::> (e) 16, is given. Which of the following correctly represents the reaction for which fj.H is the standard molar enthalpy of formation of NaCl(s)? @ (c) (d) (e) 17. 471 kJ 1O2 kJ Not enough information /t...J- Na(s) + Cl(s) ~ NaCl(s) Na(s) + (1/2)CI2(g) ~ NaCl(s) 2Na(s) + Clig) ~ 2NaCl(s) NaCl(g) ~ NaCl(s) NaOH(aq) + HCl(aq) ~ NaCl(aq) + H20(1) How much heat is required to raise the temperature of a 6.21 9 sample of iron (specific heat = 0.450 1/g/°C) from 25.0 °C to 79.8 °C? ' J (a) 70.01 (b) (c) 1011 3861 Ar=-S"4.t°<:.. {; : r ... - .=: IS":? ~ Consider the following hypothetical reactions: 18. A+B ~ AH = 200 kJ 2C L\H E-tC = -50 kJ What is Llli for the reaction A+B~2E (b) 150 kJ (c) 250 kJ (d) -250 kJ (e) -150kJ A typical ~ .le (a) ) (c) (d) (e) 20. + loO t:,.H=? 300 kJ ~ 19, "200 wavelength -"'?' 2 for infrared photon ofinfrared 2.0x10-19J 6.6 x 10-26J 25 1.5 x 10 J 6.6x 10-4°J 3.0x 102 J radiation E is 1.0 x 10-6 m. What is the energy ofa radiation ofthis wavelength? (CI. \ E = ~v:"""' \ 1'\ I ~ -~(.f J-.' ( I." )CIO 3.00)(IO ("" / I A ,c;(,J1"J -'9': 2.0 )('IO ~ -r..j),f;) Which of the following statements concerning the Bohr model of the hydrogen atom is incorrect? (a) (b) (c) States with higher values of n have higher energy . States with higher values of n have larger radius. When a hydrogen atom absorbs energy, the value of n increases. The nucleus and the orbiting electron attract one another . The ground state of a hydrogen atom has n = 0.