1. What is the main characteristic of a chemical equilibrium?
A.
The reaction stops completely
B.
The forward and reverse reaction rates become equal
C.
Only the forward reaction occurs
D.
Only the reverse reaction occurs
Correct Answer:
The forward and reverse reaction rates become equal
Explanation:
At equilibrium, the forward and reverse reactions continue simultaneously at equal rates.
2. Chemical equilibrium is said to be dynamic because:
A.
The reactants disappear completely
B.
The products disappear completely
C.
Both forward and reverse reactions continue
D.
The reaction mixture changes colour continuously
Correct Answer:
Both forward and reverse reactions continue
Explanation:
Equilibrium is dynamic because both reactions continue, even though their rates are equal.
3. At equilibrium, the concentrations of reactants and products:
A.
Become equal
B.
Remain constant with time
C.
Become zero
D.
Increase continuously
Correct Answer:
Remain constant with time
Explanation:
At equilibrium, concentrations remain constant because the forward and reverse reactions occur at equal rates.
4. For a reversible reaction to attain equilibrium, it is generally carried out in a:
A.
Closed system
B.
Vacuum only
C.
Open system with continuous removal of products
D.
System containing only products
Correct Answer:
Closed system
Explanation:
A closed system allows reactants and products to remain together so that both forward and reverse reactions can occur.
5. Which statement is true at chemical equilibrium?
A.
The amounts of reactants and products must be equal
B.
The forward reaction has stopped
C.
The reverse reaction has stopped
D.
The rates of the forward and reverse reactions are equal
Correct Answer:
The rates of the forward and reverse reactions are equal
Explanation:
Equilibrium is established when the forward and reverse reaction rates become equal, not necessarily when their amounts are equal.
6. Which macroscopic property remains constant when a system reaches equilibrium?
A.
Concentration
B.
Number of collisions only
C.
Molecular motion stops
D.
The reaction rate of the forward reaction becomes zero
Correct Answer:
Concentration
Explanation:
The concentrations of reactants and products remain constant at equilibrium, although reactions continue microscopically.
7. A reversible reaction can reach equilibrium starting with:
A.
Only reactants
B.
Only products
C.
Either reactants or products
D.
Neither reactants nor products
Correct Answer:
Either reactants or products
Explanation:
Equilibrium can be reached from either direction because both the forward and reverse reactions occur.
8. At equilibrium, the observable properties of the system are:
A.
Constant with time
B.
Always increasing
C.
Always decreasing
D.
Changing randomly
Correct Answer:
Constant with time
Explanation:
Observable properties such as colour, pressure, and concentration remain constant when equilibrium is established.
9. Which statement correctly describes the amounts of reactants and products at equilibrium?
A.
They must always be equal
B.
They are constant but need not be equal
C.
They are always zero
D.
They change continuously in the same direction
Correct Answer:
They are constant but need not be equal
Explanation:
At equilibrium, the amounts remain constant, but the quantities of reactants and products do not have to be equal.
10. What happens to the forward and reverse reaction rates as equilibrium is approached?
A.
Both rates become zero
B.
The forward rate becomes equal to the reverse rate
C.
The forward rate becomes permanently greater
D.
The reverse reaction stops completely
Correct Answer:
The forward rate becomes equal to the reverse rate
Explanation:
As equilibrium is approached, the forward and reverse rates become equal, producing no net change in composition.
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