Chemistry Practice Test: Reaction Rates and Equilibrium
- Reaction Rates and Equilibrium
- 10 questions
- 13 minutes
This test covers what makes reactions faster or slower and how reversible reactions reach equilibrium. Tip: a catalyst speeds up both the forward and reverse reactions, so it never changes the position of equilibrium.
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Question 1
A piece of zinc reacts with hydrochloric acid. Which change makes the reaction go faster?
Correct answer: B
Powder has much more surface area, so more acid particles can collide with zinc at the same time. Cooling, diluting and using larger pieces all reduce the number of effective collisions.
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Question 2
How does a catalyst speed up a reaction?
Correct answer: D
A catalyst offers an alternative route with a lower energy barrier and is not used up. It does not change the overall energy difference (ΔH) between reactants and products.
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Question 3
Why does raising the temperature usually increase the rate of a reaction?
Correct answer: A
Faster particles collide more often and, more importantly, a larger fraction of collisions have enough energy to react. Temperature changes the particles' energy, not the activation energy itself.
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Question 4
The rate law for a reaction is rate = k[A]2. What happens to the rate when the concentration of A is doubled?
Correct answer: C
The rate depends on [A] squared, so doubling [A] multiplies the rate by 22 = 4. Simple doubling would be true for a first-order reaction.
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Question 5
What is true when a reversible reaction is at equilibrium?
Correct answer: B
At equilibrium both reactions keep going at the same rate, so the amounts stop changing. The concentrations are constant, but they are usually not equal to each other.
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Question 6
Ammonia is made by N2(g) + 3H2(g) ⇌ 2NH3(g), and the forward reaction is exothermic. Which change increases the amount of NH3 at equilibrium?
Correct answer: A
Higher pressure favors the side with fewer gas molecules: 2 on the right versus 4 on the left. A catalyst only helps the system reach equilibrium faster, and raising the temperature favors the endothermic reverse reaction.
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Question 7
For an exothermic reaction at equilibrium, what happens when the temperature is raised?
Correct answer: D
Heat acts like a product in an exothermic reaction, so adding heat shifts the system back toward the reactants. Unlike a change in concentration or pressure, a change in temperature also changes the value of K.
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Question 8
What is the equilibrium constant expression for N2O4(g) ⇌ 2NO2(g)?
Correct answer: C
Products go on top and reactants on the bottom, each raised to the power of its coefficient. The coefficient 2 becomes an exponent, not a factor in front.
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Question 9
For H2(g) + I2(g) ⇌ 2HI(g), the equilibrium concentrations are [H2] = 0.10 M, [I2] = 0.10 M and [HI] = 0.80 M. What is K?
Correct answer: B
K = [HI]2 ÷ ([H2][I2]) = 0.64 ÷ 0.010 = 64. The answer 80 forgets to square [HI].
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Question 10
A reaction has an equilibrium constant K = 1 × 1010. What does this tell you?
Correct answer: D
A very large K means the numerator (products) is much bigger than the denominator (reactants) at equilibrium. K says nothing about how fast equilibrium is reached.
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