1. Which of these statements about this energy profile of a reaction mechanism i
ID: 885294 • Letter: 1
Question
1. Which of these statements about this energy profile of a reaction mechanism is true?
There are three elementary steps in this mechanism.
The first elementary step is the slow step.
The energy difference at D is the activation energy for the last step of the mechanism.
d. The overall reaction is endothermic.
2. A first order reaction is run at 298 K, and the rate constant is found to be 0.00157 s-1. The reaction is run again at 318 K and the rate constant is found to be 0.0882 s-1. What is the activation energy, Ea, in kJ, for this reaction?
4.
Which of the following is NOT a true statement concerning catalysts?
A catalyst lowers the activation energy for the reaction.
The mechanism of a reaction will change when a catalyst is added.
A catalyst decreases the temperature of the reaction which leads to a faster rate.
A catalyst is not a reactant or product in the overall reaction.
5. Which of the following statements about equilibrium is FALSE?
Equilibrium is dynamic, with both forward and reverse reactions occurring together.
At equilibrium, the concentrations of reactants and products are equal.
c. At equilibrium, the rates of the forward and reverse reactions are equal.
6. If, at a given temperature, the equilibrium constant for the reaction
Z2
Z1/2
1/Z2
1/Z1/2
a.There are three elementary steps in this mechanism.
b.The first elementary step is the slow step.
c.The energy difference at D is the activation energy for the last step of the mechanism.
d. The overall reaction is endothermic.
2. A first order reaction is run at 298 K, and the rate constant is found to be 0.00157 s-1. The reaction is run again at 318 K and the rate constant is found to be 0.0882 s-1. What is the activation energy, Ea, in kJ, for this reaction?
3. The rate law for the reaction 2A + B C + D was found to be rate = k[A]2[B]. Which of these mechanisms is consistent with this rate law?
a.A + B E + D slow
E + A C fast
b.2A E fast
E + B C + D slow
c.2A E slow
E + B C + D fast
4.
Which of the following is NOT a true statement concerning catalysts?
a.A catalyst lowers the activation energy for the reaction.
b.The mechanism of a reaction will change when a catalyst is added.
c.A catalyst decreases the temperature of the reaction which leads to a faster rate.
d.A catalyst is not a reactant or product in the overall reaction.
5. Which of the following statements about equilibrium is FALSE?
a.Equilibrium is dynamic, with both forward and reverse reactions occurring together.
b.At equilibrium, the concentrations of reactants and products are equal.
c. At equilibrium, the rates of the forward and reverse reactions are equal.
6. If, at a given temperature, the equilibrium constant for the reaction
SO3(g) SO2(g) + 1/2 O2(g)
is Z, then the equilibrium constant for the reaction
2 SO2(g) + O2(g) 2 SO3(g)
is
Z2
b.Z1/2
c.1/Z2
d.1/Z1/2
Explanation / Answer
2. A first order reaction is run at 298 K, and the rate constant is found to be 0.00157 s-1. The reaction is run again at 318 K and the rate constant is found to be 0.0882 s-1. What is the activation energy, Ea, in kJ, for this reaction?
Solution :-
Using the Arrhenius equation we can calculate the activation energy as follows
Ln[k2/k1] = Ea/R [(1/T1)-(1/T2)]
Lets put the values in the formula
R= constant = 8.314 J permol K
ln[0.0882/0.00157] = Ea /8.314 J per mol K [(1/298)-(1/318)]
4.028 = Ea/8.314 J per mol K *0.000211
4.028 * 8.314 J permol K /0.000211 K = Ea
158676 J per mol = Ea
Lets convert joules to kJ
158676 J per mol * 1 kJ / 1000 J = 158.7 kJ / mol
Therefore activation energy= 158.7 kJ/mol
3. The rate law for the reaction 2A + B C + D was found to be rate = k[A]2[B]. Which of these mechanisms is consistent with this rate law?
Solution :-
Since rate law is
Rate = k [A]^2[B]
This means reaction is second order with A and first order with B
Therefore the mechanism given in the option a is the constant with the rate law
That is
A+B -- E+Dslow
E+A -----> Cfast
So the correct answer is option‘a’
4 Which of the following is NOT a true statement concerning catalysts?
Solution :- Catalyst decreases the activation energy , it alters the mechanism also the catalyst recovered at the end of reaction means its not reactant nor product so the incorrect statement is option ‘c’ that is A catalyst decreases the temperature of the reaction which leads to a faster rate
5. Which of the following statements about equilibrium is FALSE?
Solution :-
Equilibrium is the dynamic state where the forward and backward reaction have same rate
Therefore the incorrect statement is option ‘b’ that is At equilibrium, the concentrations of reactants and products are equal
Q6 solution:-
For the forward reaction the rate constant is Z
When the reaction is reversed then we take the inverse of the rate constant of the orginal reaction therefore the rate constant for the reverse reaction is Kreverse = 1/Z^2
So the correct answer is option ‘c’
It is squared because reaction is doubled.
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