Q. For a first-order reaction, if the half-life is 10 minutes, what will be the half-life if the concentration is doubled?
A.
10 minutes
B.
20 minutes
C.
5 minutes
D.
It cannot be determined
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Solution
The half-life of a first-order reaction is independent of concentration; it remains 10 minutes.
Correct Answer:
A
— 10 minutes
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Q. For a zero-order reaction, how does the concentration of reactant affect the rate?
A.
Rate is directly proportional to concentration
B.
Rate is inversely proportional to concentration
C.
Rate is independent of concentration
D.
Rate decreases with increasing concentration
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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
— Rate is independent of concentration
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Q. If the concentration of a reactant is halved in a first-order reaction, what happens to the rate?
A.
Rate is halved
B.
Rate is doubled
C.
Rate remains the same
D.
Rate is quartered
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Solution
In a first-order reaction, the rate is directly proportional to the concentration of the reactant. Halving the concentration will halve the rate.
Correct Answer:
A
— Rate is halved
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Q. If the rate constant of a reaction doubles when the temperature increases by 10°C, what is the approximate activation energy?
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 and the rule of thumb that a 10°C increase roughly doubles the rate constant, we can estimate the activation energy to be around 40 kJ/mol.
Correct Answer:
B
— 40 kJ/mol
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Q. If the rate constant of a reaction doubles when the temperature increases 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 doubling of the rate constant corresponds to an activation energy of approximately 40 kJ/mol for a 10°C increase.
Correct Answer:
B
— 40 kJ/mol
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Q. In a reaction at equilibrium, what happens if the concentration of a reactant is increased?
A.
The equilibrium shifts to the right
B.
The equilibrium shifts to the left
C.
The equilibrium remains unchanged
D.
The reaction stops
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Solution
According to Le Chatelier's principle, increasing the concentration of a reactant shifts the equilibrium to the right, favoring product formation.
Correct Answer:
A
— The equilibrium shifts to the right
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Q. What is the rate law for a reaction that is second order with respect to A and first order with respect to B?
A.
Rate = k[A][B]
B.
Rate = k[A]^2[B]
C.
Rate = k[A]^2
D.
Rate = k[A][B]^2
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Solution
The rate law is determined by the orders of the reactants. For second order in A and first order in B, the rate law is Rate = k[A]^2[B].
Correct Answer:
B
— Rate = k[A]^2[B]
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Q. What is the relationship between the rate of a reaction and the concentration of reactants in a first-order reaction?
A.
Rate is proportional to the square of the concentration
B.
Rate is inversely proportional to the concentration
C.
Rate is directly proportional to the concentration
D.
Rate is independent of the concentration
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Solution
In a first-order reaction, the rate is directly proportional to the concentration of the reactant.
Correct Answer:
C
— Rate is directly proportional to the concentration
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