Chemical Kinetics
Q. For a first-order reaction, if the half-life is 10 minutes, what will be the half-life if the initial concentration is doubled?
A.
10 minutes
B.
5 minutes
C.
20 minutes
D.
15 minutes
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Solution
For a first-order reaction, the half-life is independent of the initial concentration. Therefore, it remains 10 minutes.
Correct Answer: A — 10 minutes
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Q. For a first-order reaction, the half-life is independent of the initial concentration. What is the expression for half-life?
A.
t1/2 = 0.693/k
B.
t1/2 = k/0.693
C.
t1/2 = 1/k
D.
t1/2 = k/2
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Solution
For a first-order reaction, the half-life is given by the expression t1/2 = 0.693/k.
Correct Answer: A — t1/2 = 0.693/k
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Q. For a first-order reaction, the half-life is independent of which of the following?
A.
Initial concentration
B.
Rate constant
C.
Temperature
D.
All of the above
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Solution
For a first-order reaction, the half-life is independent of the initial concentration.
Correct Answer: A — Initial concentration
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Q. For a reaction A → B, if the rate of formation of B is 0.5 mol/L/s, what is the rate of disappearance of A?
A.
0.5 mol/L/s
B.
1.0 mol/L/s
C.
0.25 mol/L/s
D.
2.0 mol/L/s
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Solution
The rate of disappearance of A is equal to the rate of formation of B, multiplied by the stoichiometric coefficients. Here, it is 1.0 mol/L/s.
Correct Answer: B — 1.0 mol/L/s
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Q. For a reaction A → B, if the rate of reaction doubles when the concentration of A is doubled, what is the order of the reaction with respect to A?
A.
Zero order
B.
First order
C.
Second order
D.
Third order
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Solution
If doubling the concentration of A doubles the rate, the reaction is first order with respect to A.
Correct Answer: B — First order
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Q. For a zero-order reaction, how does the rate change with concentration?
A.
Increases linearly
B.
Decreases linearly
C.
Remains constant
D.
Increases exponentially
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Solution
In a zero-order reaction, the rate is constant and does not depend on the concentration of reactants.
Correct Answer: C — Remains constant
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Q. For a zero-order reaction, how does the rate change with respect to concentration?
A.
Increases linearly
B.
Decreases linearly
C.
Remains constant
D.
Increases exponentially
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Solution
In a zero-order reaction, the rate is constant and does not depend on the concentration of the reactants.
Correct Answer: C — Remains constant
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Q. If the activation energy of a reaction is increased, what happens to the rate constant k?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
According to the Arrhenius equation, an increase in activation energy results in a decrease in the rate constant k.
Correct Answer: B — Decreases
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Q. If the rate of a reaction doubles when the temperature is increased by 10°C, what is the approximate activation energy (Ea) of the reaction?
A.
20 kJ/mol
B.
40 kJ/mol
C.
60 kJ/mol
D.
80 kJ/mol
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Solution
Using the Arrhenius equation, a rule of thumb states that for every 10°C increase in temperature, the rate doubles if Ea is around 40 kJ/mol.
Correct Answer: B — 40 kJ/mol
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Q. In a first-order reaction, if the concentration of the reactant is halved, what happens to the half-life?
A.
It doubles
B.
It remains the same
C.
It is halved
D.
It becomes zero
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Solution
In a first-order reaction, the half-life is independent of the concentration of the reactant, so it remains the same.
Correct Answer: B — It remains the same
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Q. In a reaction A → B, if the concentration of A decreases from 0.5 M to 0.1 M in 20 minutes, what is the average rate of reaction?
A.
0.02 M/min
B.
0.04 M/min
C.
0.05 M/min
D.
0.06 M/min
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Solution
Average rate = (change in concentration) / (time) = (0.5 - 0.1) / 20 = 0.02 M/min.
Correct Answer: B — 0.04 M/min
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Q. In a reaction A → B, if the rate of formation of B is 0.1 mol/L·s, what is the rate of disappearance of A?
A.
0.1 mol/L·s
B.
0.05 mol/L·s
C.
0.2 mol/L·s
D.
0.1 L/mol·s
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Solution
For the reaction A → B, the rate of disappearance of A is equal to the rate of formation of B, hence it is 0.1 mol/L·s. However, if stoichiometry is considered as 1:1, the rate of disappearance of A is also 0.1 mol/L·s.
Correct Answer: C — 0.2 mol/L·s
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Q. In a reaction A → B, if the rate of formation of B is 0.5 mol/L·s, what is the rate of disappearance of A?
A.
0.5 mol/L·s
B.
1.0 mol/L·s
C.
0.25 mol/L·s
D.
0.75 mol/L·s
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Solution
For the reaction A → B, the rate of disappearance of A is equal to the rate of formation of B, thus it is 1.0 mol/L·s.
Correct Answer: B — 1.0 mol/L·s
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Q. In a reaction mechanism, the slowest step is known as the:
A.
Rate-determining step
B.
Intermediate step
C.
Fast step
D.
Catalytic step
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Solution
The slowest step in a reaction mechanism is called the rate-determining step, as it controls the overall reaction rate.
Correct Answer: A — Rate-determining step
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Q. In a reaction mechanism, the slowest step is known as what?
A.
Rate-determining step
B.
Intermediate step
C.
Fast step
D.
Catalytic step
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Solution
The slowest step in a reaction mechanism is known as the rate-determining step.
Correct Answer: A — Rate-determining step
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Q. In a zero-order reaction, how does the rate change with respect to concentration?
A.
Increases linearly
B.
Decreases linearly
C.
Remains constant
D.
Increases exponentially
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Solution
In a zero-order reaction, the rate is constant and does not depend on the concentration of reactants.
Correct Answer: C — Remains constant
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Q. In a zero-order reaction, if the rate constant k is 5 mol/L/s, how long will it take for the concentration to decrease from 2 mol/L to 0 mol/L?
A.
0.4 s
B.
0.5 s
C.
0.6 s
D.
0.8 s
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Solution
For a zero-order reaction, time = (initial concentration - final concentration) / k = (2 - 0) / 5 = 0.4 s.
Correct Answer: C — 0.6 s
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Q. In a zero-order reaction, the rate of reaction is independent of which of the following?
A.
Concentration of reactants
B.
Temperature
C.
Catalyst
D.
All of the above
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Solution
In a zero-order reaction, the rate of reaction is independent of the concentration of reactants.
Correct Answer: A — Concentration of reactants
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Q. The Arrhenius equation relates the rate constant to which of the following?
A.
Temperature and concentration
B.
Temperature and activation energy
C.
Concentration and pressure
D.
Temperature and volume
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Solution
The Arrhenius equation relates the rate constant to temperature and activation energy.
Correct Answer: B — Temperature and activation energy
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Q. The half-life of a first-order reaction is dependent on which of the following?
A.
Initial concentration
B.
Rate constant
C.
Temperature
D.
All of the above
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Solution
The half-life of a first-order reaction is given by t1/2 = 0.693/k, which depends only on the rate constant.
Correct Answer: B — Rate constant
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Q. The rate law for a reaction is determined experimentally and is dependent on which of the following?
A.
Stoichiometry of the reaction
B.
Mechanism of the reaction
C.
Equilibrium constant
D.
Temperature only
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Solution
The rate law for a reaction is determined experimentally and is dependent on the mechanism of the reaction.
Correct Answer: B — Mechanism of the reaction
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Q. The rate law for a reaction is determined experimentally. Which of the following is true?
A.
It can be derived from stoichiometry
B.
It is always first-order
C.
It depends on the mechanism
D.
It is independent of temperature
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Solution
The rate law for a reaction depends on the mechanism of the reaction.
Correct Answer: C — It depends on the mechanism
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Q. The rate law for a reaction is given as rate = k[A][B]². What is the overall order of the reaction?
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Solution
The overall order of the reaction is the sum of the powers of the concentration terms, which is 1 + 2 = 3.
Correct Answer: C — 3
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Q. The rate of a reaction doubles when the temperature is increased by 10°C. This is an example of which rule?
A.
Arrhenius equation
B.
Van 't Hoff rule
C.
Le Chatelier's principle
D.
Gibbs free energy
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Solution
This is an example of Van 't Hoff rule, which states that the rate of reaction doubles for every 10°C increase in temperature.
Correct Answer: B — Van 't Hoff rule
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Q. The rate of a reaction is defined as the change in concentration of a reactant or product per unit time. What is the unit of rate?
A.
mol/L
B.
mol/L·s
C.
L/mol·s
D.
1/s
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Solution
The rate of reaction is expressed in terms of concentration change per unit time, hence the unit is mol/L·s.
Correct Answer: B — mol/L·s
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Q. The rate of a reaction is directly proportional to the product of the concentrations of the reactants raised to their respective powers. This is known as what?
A.
Rate law
B.
Equilibrium constant
C.
Reaction quotient
D.
Catalytic law
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Solution
This relationship is known as the rate law of the reaction.
Correct Answer: A — Rate law
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Q. What effect does increasing the concentration of a reactant have on the rate of a first-order reaction?
A.
Increases the rate
B.
Decreases the rate
C.
No effect
D.
Rate becomes zero
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Solution
Increasing the concentration of a reactant in a first-order reaction increases the rate of the reaction.
Correct Answer: A — Increases the rate
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Q. What is the effect of a catalyst on the equilibrium position of a reversible reaction?
A.
Shifts the equilibrium to the right
B.
Shifts the equilibrium to the left
C.
No effect on equilibrium position
D.
Increases the equilibrium constant
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Solution
A catalyst does not affect the position of equilibrium; it only speeds up the rate at which equilibrium is reached.
Correct Answer: C — No effect on equilibrium position
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Q. What is the effect of increasing temperature on the rate of a chemical reaction?
A.
Decreases the rate
B.
Increases the rate
C.
No effect
D.
Depends on the reaction
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Solution
Increasing temperature generally increases the rate of a chemical reaction.
Correct Answer: B — Increases the rate
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Q. What is the effect of increasing the concentration of a reactant in a first-order reaction?
A.
Rate increases linearly
B.
Rate decreases
C.
Rate remains constant
D.
Rate increases exponentially
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Solution
In a first-order reaction, increasing the concentration of a reactant results in a linear increase in the rate.
Correct Answer: A — Rate increases linearly
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