1. A solution containing 100.0 g of an unknown liquid and 900.0 g of water has a
ID: 876603 • Letter: 1
Question
1. A solution containing 100.0 g of an unknown liquid and 900.0 g of water has a freezing point of -3.33 oC. Given Kf = 1.86 oC/m for water, what is the molecular weight of the unknown.
2.
. Consider the reaction of peroxydisulfate ion, S2O8-2, with iodide ion, I-, in aqueous solution:
S2O8-2(aq) + 3 I- (aq) à 2SO4-2(aq) + I3- (aq)
At a particular temperature, the rate of this reaction varies with reactant concentrations in the following manner:
Experiment # [S2O8-2] (M) [I-] (M) Intial rate (M/s)
1 0.038 0.060 1.4 x 10-5
2 0.076 0.030 1.4 x 10-5
3 0.076 0.060 2.8 x 10-5
a) Write the rate law for this reaction.
b) What is the value of the rate constant for this reaction?
c) What is the overall order for this reaction?
3. The following data were collected for the rate of disappearance of NO in the reaction:
2 NO (g) + O2 (g) à 2 NO2 (g)
Experiment [NO] (M) [O2] (M) Initial Rate (M/s)
1 0.0126 0.0125 1.41 x 10-2
2 0.0252 0.0250 1.13 x 10-1
3 0.0252 0.0125 5.64 x 10-2
a) Determine the rate law for this reaction.
b) What is the value of the rate constant?
c) What is the overall order for this reaction?
4. The following data were measured for the reaction:
BF3 (g) + NH3 (g) à F3B-NH3 (g)
Exp. [BF3] (M) [NH3] (M) Initial Rate (M/s)
1 0.200 0.100 0.0682
2 0.350 0.100 0.1193
3 0.175 0.100 0.0596
4 0.250 0.250 0.2130
5 0.250 0.125 0.1065
a) What is the rate law for the reaction? Show your work.
b) What is the overall order of the reaction?
c) What is the value of the rate constant for the reaction? (4 pts)
Explanation / Answer
1-delta Tf= 3.33 Kf=1.86, m= molality
delta Tf= Kf x m=> m= delta Tf / Kf= 1.790
amount of substance= 0.9 kg of water x 1.79 /1 kg of water=1.611m solute
moleculer wt. of unknown compound is = 100/1.611= 62.07g/mol
2-a- rate= K[S2O8-2]^1[I-]^1
b-[S2O8--]=0.076M, [I-]= 0.06M, rate=2.8x10^-5M/s
K= rate / [S2O8-2]^01[3I-]^1 = 2.8x10^-5 / 0.06x0.076 = 6.14 x10^-3 M^-1s^-1
c- this is 2st oder reaction.=>1+1=2
3-rate law is deduce by camparing concentration of reactant and rate of reaction keeping concentration of one reactant constant.
a-rate law=
rate = K [NO]^2[O2]^1
c- oder of reaction= 2+1 = 3
b- K= rate / [NO]^2[O2]^1 = 1.41x10^-2 / [0.0126]^2[0.0125]= 1.41x10^-2 //1.9845x10^-6=0.7105x10^4=7.1x10^4
4-a--rate law
comparing eq.1 & eq.2 rate is increase by 1.75 times as we increases con. of BF3 1.75times
so rate is 1st oder for BF3,
comparing eq.3 & eq.4 rate is reduced by 1/2 as con. of NH3 is reduced by 1/2
so rate is first oder for NH3
rate =K [BF3]^1[NH3]^1
b- over all oder of reaction = 1+1 = 2
c-K= rate / [BF3][NH3]= 0.0682 / [.200][.100] = 3.41M^-1s^-1
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