Name:_____________
(4 points)
Chemistry 114
Third Hour Exam
Remember- Show all work for partial credit
All questions are worth 12 points
1. Consider the reaction
4PH3(g) 6P4(g) + 6H2(g)
If .0048 moles of PH3 was consumed in a 1.5L container in the first second of the
reaction:
A. What is the rate of PH3 consumption in Moles/L@sec?
B. What is the rate of P4 production in Mole/L@sec?
C. What is the rate of H2 production in grams/L@minute?
2. I am studying the reaction: A + B 6 C
Given the following data of concentration and rates:
[A](M) [B](M)
rate (mol/L@sec)
.70
.70
.345
1.0
.70
.548
1.0
1.4
.548
Find the order parameters and the rate constant for this reaction. When you have
found these numbers write the rate law for this reaction.
3. When I study the concentration of a product as a function of time, I obtain the
following three plots:
From the data in the above plots
Determine the order parameter for this reaction with respect to this reactant.
Plot of ln[ ] vs time is linear, so order parameter must be 1
Determine the rate constant for this reaction.
-k = slope of line = Äy/Äx
=(-7.5-(-4.6))/(580-0); -k = -2.9/580; k=.005
Write the rate law for this reaction including your calculated rate constant and
order parameter.
Rate = k[ ]1
4. If the initial concentration of a reactant is 0.15 M, and it takes 25 minutes for this
concentration to drop to .075 M.
A. If the reaction is zero order, what is the k for this reaction?
t1/2=[ ]0/2k; 25min=0.15M/2k; k=.15M/2(25min); .003mol/L@min
B. If the reaction is first order, what is the k for this reaction?
t1/2=.693/k; 25min=.693/k; k=.693/25min = .02772min-1
C. If the reaction is second order, what is the k for this reaction?
t1/2= 1/k[ ]0; 25min=1/k(.15M); k=1/(25min@.15M); k=.2667L/mol@min
5. A proposed mechanism for a reaction is:
C4H9Br 6C4H9+ + BrC4H9+ + H2O 6 C4H9OH2+
C4H9OH2+ +H2O 6 C4H9OH + H3O+
Slow
Fast
Fast
A. Write the rate law expected for this mechanism
Using the molecularity of slow reaction
rate = k[C4H9Br]
B. What is the overall balanced equation for this reaction
C4H9Br + C4H9+ + H2O + C4H9OH2+ + H2O 6C4H9+ + Br- + C4H9OH2+ + C4H9OH + H3O+
C4H9Br+ 2 H2O 6 Br- + C4H9OH + H3O+
C. Are there any intermediates in this reaction? If so, what are the
intermediates?
C4H9 , C4H9OH2++
6. In class I told you about the chemists model for reaction kinetics. Using this model it
was proposed that ...
What do each of the symbols in the above equation represent?
k=rate of a reaction
z = number of collisions
ñ = stearic factor -fraction of collisions with proper orientation
e = exponential function or the inverse of the natural log
Ea = activation energy
R = the gas constant in Joules/K@mol
T = Temperature in K
7. Write the equilibrium expressions for the following reactions:
CH3COOH(aq) + H2O(l) W CH3COO- (aq) + H3O+(aq)
4PH3(g) 6P4(g) + 6H2(g)
2 PbS (s) +3O2(g) W 2PbO(s) + 2SO2(g)
8. Given that the equilibrium constant (in terms of concentration) is 8.96x10-2 for the
reaction PCl5(g) W PCl3(g) + Cl2(g)
Determine the equilibrium constants for the following reactions:
PCl3(g) + Cl2(g) W PCl5(g)
Reverse of original reaction, Knew = 1/Korg
Knew=1/8.96x10-2 = 11.16
3PCl5(g) W3PCl3(g) + 3Cl2(g)
Coefficients of new equation = 3 x original equation
Knew = Korg3
Knew = (8.96x10-2)3
= 7.19x10-4
PCl5(g) W PCl3 (g)+ Cl2(g) in terms of pressure, when the temperature is 100K.
KP =KC(RT)Än; Än=2-1 = 1
=8.96x10-2(.08206@100)1
=.735