answers to midterm #1

answers to midterm #1 - ntil tQ,.*tf I *hl,tc 1. GaseousABz...

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ntil tQ,.* tf I *hl,tc 1. Gaseous ABz is placed in a6.0 L closed container and held constant at 480 K. Eventually equilibrium is established, and this equilibrium contains a mixture of gaseous Az, Bz and ABz in the reaction vessel, the result of an exothermic reaction. The equilibrium concentration of ABz is determined to be 3.0 M, and the equilibrium concentration of Bz is determined to be 4.0 M. a) (4 points) Complete the balanced reaction occurring in the flask in the space indicated below, being sure to indicate the state of each product. Using the table provided, list the initial and equilibrium concentrations of each compound. Initial Equilibrium IAzl 0 2.0 lBrl 0 4.0 IABz1 7.0 3.0 b) (3 points) Using the plot below, construct concentration vs. time profiles for each compound. Label the correct curve on the plot as [ABz] ,f,Arl, and lBrl, and indicate with a dotted line on your plot where equilibrium is first reached. tl (2 points) Calculate Kp for this reaction at 480 K. 2 ABz(g)- Az(g) +2Bz(g) I 7.0 0 0 C -4.0 +2.0 +4.0 E 3.0 2.0 4.0 time, arb. units c) rc = qf )c1.oJ' - },b { roJ' 0'o) L tcp 3 ).L K (o,otlor? K Chem 1C midterm #1
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d) (4 points) Using the table provided on the right, determine what effect, tf any, the indicated changes would have on the reaction in 1a. Write "left", "right" or "none" to indicate shifts in the reaction, and "increases" r "decreases" or "r.or.e" for changes in Kp. Change Direction of shift? Change in Kp ABz is added right none Volume changed to 1.0 L left none Temp changed to 100 K right lncreases 2. Cas phase nitrogen dioxide establishes an equilibrium with gas phase dinitrogen tetroxide (NzO+), with Kp = 1.33 at 300.0 K. 2.00 atm of NOz are placed into a 4.00 L flask and allowed to come to equilibrium. a) (4 points) SET UP BUT DO NOT SOLVE the Kn expression involving a variable "x" that could be used to determine the equilibrium pressures of both gases. Your reaction should have NOz as the reactant. ) tuor,Cj) * Nao.{ cl) t4 z l.I] I n.$s C -LK g L-Lr o +K X e-Y(es) r on : b) (2 points) When the above equation is solved using the quadratic formula, the two possible roots of the equation are x = 0.65 and x - 1.54. Which root should be used to determine the equilibrium pressures? Explain your answer. No points awarded without an explanation. 0.65 is the correct root to use, since using 1.54 in the ICE table as defined aboae results in a negatizte equilibrium pressure for NOz Q - 2x1.54 = -1.08 atm). This is impossible, thus zae discard x = L.54 as a possible solution. Chem 7C midterm #7
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answers to midterm #1 - ntil tQ,.*tf I *hl,tc 1. GaseousABz...

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