Q. For 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 will shift the equilibrium position to the right, favoring the formation of products.
Correct Answer:
A
— The equilibrium shifts to the right
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Q. For a reaction with a rate constant of 0.1 s^-1, what is the half-life for a first-order reaction?
A.
0.693 s
B.
6.93 s
C.
10 s
D.
0.1 s
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Solution
The half-life for a first-order reaction is given by t1/2 = 0.693/k. Thus, t1/2 = 0.693/0.1 = 6.93 s.
Correct Answer:
A
— 0.693 s
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Q. In a reaction mechanism, what is an intermediate?
A.
A reactant that is consumed in the final product
B.
A product that is formed and then consumed
C.
A catalyst that speeds up the reaction
D.
A transition state of the reaction
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Solution
An intermediate is a species that is formed during the reaction and consumed in subsequent steps, not appearing in the overall reaction.
Correct Answer:
B
— A product that is formed and then consumed
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Q. What is the effect of increasing the surface area of a solid reactant on the reaction rate?
A.
No effect on the rate
B.
Decreases the rate
C.
Increases the rate
D.
Only affects gas-phase reactions
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Solution
Increasing the surface area of a solid reactant increases the rate of reaction by providing more area for collisions.
Correct Answer:
C
— Increases the rate
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Q. What is the effect of temperature on the rate constant of a reaction according to the Arrhenius equation?
A.
Rate constant decreases with temperature
B.
Rate constant increases with temperature
C.
Rate constant is unaffected by temperature
D.
Rate constant is only affected by activation energy
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Solution
According to the Arrhenius equation, an increase in temperature generally leads to an increase in the rate constant, k.
Correct Answer:
B
— Rate constant increases with temperature
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Q. What is the primary role of a catalyst in a chemical reaction?
A.
Increase the concentration of reactants
B.
Lower the activation energy
C.
Change the equilibrium position
D.
Increase the temperature of the reaction
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Solution
A catalyst lowers the activation energy of a reaction, thereby increasing the rate without being consumed.
Correct Answer:
B
— Lower the activation energy
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Q. What is the term for the minimum energy required for a reaction to occur?
A.
Enthalpy
B.
Entropy
C.
Activation energy
D.
Gibbs free energy
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Solution
The minimum energy required for a reaction to occur is known as the activation energy.
Correct Answer:
C
— Activation energy
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Q. Which of the following statements about reaction rates is true?
A.
Reaction rates are always constant
B.
Reaction rates can change with time
C.
Reaction rates are independent of temperature
D.
Reaction rates are only affected by concentration
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Solution
Reaction rates can change with time as reactants are consumed and products are formed, affecting the concentration of reactants.
Correct Answer:
B
— Reaction rates can change with time
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