A reaction has the rate equation rate = k². What is the overall order of the reaction?
Correct answer B. 3
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MDCAT ECAT Chemistry MCQs
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For rate = k², how does the rate change if is doubled and is halved at the same time?
Correct answer D. It becomes twice as fast
What are the units of the rate constant for a second-order reaction?
Correct answer B. dm³ mol⁻¹ s⁻¹
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Which units correspond to the rate constant of a zero-order reaction?
Correct answer C. mol dm⁻³ s⁻¹
Which statement about the half-life of a first-order reaction is correct?
Correct answer D. It is independent of the initial concentration of the reactant
A first-order reaction has a rate constant of 0.0231 min⁻¹. What is its half-life?
Correct answer B. 30 min
A first-order reactant has a half-life of 10 min. If 80 g is present initially, what mass remains after 30 min?
Correct answer B. 10 g
Which statement best defines activation energy?
Correct answer C. The minimum extra energy that colliding reactant particles need to form the activated complex
Which statement about the activated complex is correct?
Correct answer C. It is a short-lived, high-energy arrangement at the top of the energy barrier
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How does a catalyst increase the rate of a reaction?
Correct answer A. It provides an alternative pathway with a lower activation energy
What is the main reason that a small rise in temperature greatly increases the rate of most reactions?
Correct answer B. The fraction of molecules with energy equal to or greater than the activation energy rises sharply
Why does powdered calcium carbonate react faster with dilute HCl than an equal mass of marble chips?
Correct answer C. The powder has a larger surface area, giving more frequent collisions
For a given reaction, the value of the rate constant k depends on ____.
Correct answer D. temperature
For H₂(g) + I₂(g) ⇌ 2HI(g), the equilibrium concentrations are = 0.10, = 0.10 and = 0.70 mol dm⁻³. What is Kc?
Correct answer C. 49
For which equilibrium is Kp equal to Kc at any temperature?
Correct answer B. H₂(g) + I₂(g) ⇌ 2HI(g)
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What is the effect of adding an inert gas such as argon to an equilibrium mixture of gases at constant volume?
Correct answer B. There is no change in the equilibrium position
What are the units of Kc for the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?
Correct answer D. mol⁻² dm⁶
Under which condition will a precipitate of a sparingly soluble salt form when two solutions are mixed?
Correct answer A. When the ionic product exceeds the Ksp of the salt
After mixing, a solution contains = 1.0 × 10⁻³ and = 1.0 × 10⁻³ mol dm⁻³. Given Ksp(BaSO₄) = 1.1 × 10⁻¹⁰, what happens?
Correct answer A. The ionic product is 1.0 × 10⁻⁶, so BaSO₄ precipitates
What does a very large value of Kc, such as 10¹², indicate about a reaction?
Correct answer D. At equilibrium the mixture consists mainly of products