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Unformatted text preview: I. II. III. IV. , Chemistry 1A
Practice Problems for Examination II (15 Points)
Calculate the pressure, in atrn., exerted by 1.82 mols of sulfur hexaﬂuoride (SF 6) at a temperature of 695°C, in a vessel with a volume of 5.43 L.
PV = "RT P __ "RT _ (1.82mol)(0.0821L~at7n/Kvmol)(69.5+273)K _ 9 42am (20 Points)
Sodium azide, NaNg, decomposesas follows:
2NaNH3(s) —» 3N2(g) + 2Na(s)
What volume (in liters), at 21° C and 823 torr (mm Hg), of nitrogen will be produced by
the decomposition of 60.0 g of sodium azide? molestaNa = $51; = 0.923__moles, 2moles =9 3moles,
x _ 3 IBSN _ _ '
0.923molesNaN3 " Miami ’ x _ 2 x 0923 “ 1'38mOIeSN2
_ _ (1.38 1 )(0.03206L.axm/ le-K)(294K) __
V — 11% _ m0 2:823mn'l'76010n'z‘12n) — (20 Points)
Given the following reaction:
N2(g)+3H2(g)22NH3(g) K=KP =1.45><10‘S atSOOOC. At equilibrium, the partial pressure of H 2 is 0.920 atm and the partial pressure of N 2 is
0.432 atm. What is the equilibrium partial pressure of NH 3 ? N2(g) + 3H2(g) 4—3- 2NH3(g)
Equil: 0.432 0.928 x
KmﬁL— x2 =1.45><10~5 PmPin " m
x2 = (1.45 ><10‘5)(0.432)(0.928)3 = 5.01 x 10-?
x —- 45.01x10‘ = 2.24 x10‘3atm =PNH3
Brief Answers (25 Points Total, Credit as Indicated)
A. (5 Points)
. What is the volume in liters of 1.00 mole of an ideal gas at STP? V = n x 22.4%,— : 1.00mol x 22.43% = 22.4L
B. (10 Points, 5 Points Each Part)
Given the equilibrium: CaC03(S) z! Ca0(s) + C02(g) At a temperature of 800°C, the pressure of C02(g) is 0.236 atm.
1. What is K, for this reaction? KP =pc02 = 0.236,
2. What is the value of the molarity-based equilibrium constant, KC reaction? T = 800 +273 = 1073K, Kc = (R134, , Kc = Elﬁn?) = 2.68 ><10‘3
C. ‘ (5 Points)
What is the molarity-based equilibrium constant for the following reaction
2N0(E) + 02(E) Tl 2N02(g) if the following concentrations are found at equilibrium? [N0] = 0.0542M,  = 0.127M, [N02] = 15.5M
(15.5)2 Chemistry 1A
Practice Problems for Examination II Page #2 (5 Points)
A 452 mL sample of an ideal gas is heated from 22°C to 187°C at constant
pressure. What is the ﬁnal volume of the gas? i—I=%§= T1=22+273=295K, T2=187+273=46OK
V2 = V1X% =452mLx§3$51§ -_—. 705mL V. (20 Points, 5 Points Each Part)
Multiple Choice. Circle the letter which represents the best response to each question.
Only one response is correct. No partial credit. (The letter of the correct response is bold, italic, and capital.)
1 . .a. A glass tube is ﬁlled with mercury and inverted in a pool of mercury. The
mercury column stabilizes at a height of 735 mm above the pool of mercury.
What is the pressure of the atmosphere? a. 0.697 atm, b. 0.735 atm, C. 0.967 atm, d. 1.03 atm, e. 194 atm For the reaction 2H2(g) + 02(g) Z 2H20(g), what is the relationship between K c
and K P ? a. K c = KP C. K c = K P(RT) e. None of the above. b. K = 192(an
d. KP = KC(RT)2 For the hypothetical reactions 1 and 2 below, K 1 = 103 and K 2 = 10-5. What is
the value of K for reaction 3? .
l: A+2B2AB2 2: A+BZAB
A. 10‘8 b. 10'2 c.102 3: AB: 2 AB +B
d. 103 e. None of these. What is the equilibrium constant expression for the reaction . CaCl2(s) + 2H20(g) Z CaClz . 2H20(s)
[CaCl 21W 20] 1
1 c' 2[H20]
d. [H 20]2
e. None of the above. ...
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- Spring '08