Q: A reaction mechanism consists of the following steps: Step 1: $$\mathrm{A + B \rightarrow C} ($$slow) Step 2: $$\mathrm{C + D \rightarrow E} ($$fast) What is the rate-determining step and what is the rate law for the overall reaction?

Step 1 is the rate-determining step; rate law: $$\text{rate} = k[\mathrm{A}][\mathrm{B}]$$

Question 1

Which of the following best explains why the rusting of the boat in the image is considered a slow chemical reaction?

Accepted Answer

The activation energy for rusting is high, and the frequency of effective collisions between iron and oxygen is low.

Question 2

According to collision theory, which factor would NOT increase the rate of rust formation on the boat?

Accepted Answer

Decreasing the surface area of exposed iron.

Question 3

The formation of stalactites and stalagmites in caves, as shown in the image, is an example of which type of chemical process?

Accepted Answer

A reversible reaction reaching dynamic equilibrium.

Question 4

Which of the following best describes dynamic equilibrium in the context of stalactite and stalagmite formation?

Accepted Answer

The forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.

Question 5

Given the reaction: $$\mathrm{$$CaCO_3$$(s) \rightleftharpoons Ca$$^{2+}$$(aq) + CO_3$^{2-}(aq)}$$, write the equilibrium constant expression $$K_c$$ for this reaction.

Accepted Answer

$$K_c = [\mathrm{Ca$$^{2+}$$}][\mathrm{CO_3$^{2-}}]$$

Question 6

A reaction has a rate law: $$	ext{rate} = k[\mathrm{A}]^2[\mathrm{B}]. If $$the concentration of A is doubled and B is halved, by what factor does the rate change?

Accepted Answer

The rate increases by a factor of 2.

Question 7

Which of the following statements about catalysts is correct?

Accepted Answer

A catalyst lowers the activation energy, increasing the rate of both the forward and reverse reactions.

Question 8

For a first-order reaction, the half-life is given by $$t_{1/2} = \frac{0.693}{k}. If $$the rate constant $$k is $$doubled, what happens to the half-life?

Accepted Answer

The half-life is halved.

Question 9

Which of the following would NOT affect the value of the equilibrium constant $$K$$ for a given reaction?

Accepted Answer

Adding a catalyst.

Question 10

A reaction mechanism consists of the following steps:

Step 1: $$\mathrm{A + B \rightarrow C} ($$slow)
Step 2: $$\mathrm{C + D \rightarrow E} ($$fast)

What is the rate-determining step and what is the rate law for the overall reaction?

Accepted Answer

Step 1 is the rate-determining step; rate law: $$	ext{rate} = k[\mathrm{A}][\mathrm{B}]$$

Question 11

The Arrhenius equation is $$k = Ae$$^{-E_a/(RT)}$$. If the activation energy E_a$ is decreased, what is the effect on the rate constant k$?

Accepted Answer

The rate constant $$k$$ increases.

Question 12

Which of the following best describes the effect of increasing temperature on a reaction at equilibrium?

Accepted Answer

It shifts the equilibrium position in the direction that absorbs heat (endothermic direction).

Question 13

For the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, what is the expression for the equilibrium constant $$K_c$$?

Accepted Answer

$$K_c = \frac{[\mathrm{NH_3$}]^2}{[\mathrm{N_2$}][\mathrm{H_2$}]^3}$$

Question 14

A reaction is found to be second order overall. Which of the following could be a possible rate law?

Accepted Answer

$$	ext{rate} = k[\mathrm{A}]^2$$

Question 15

If the reaction quotient $$Q$$ for a system is less than the equilibrium constant $$K$$, what will happen as the system moves toward equilibrium?

Accepted Answer

The forward reaction will proceed to form more products.

Question 16

Which of the following is a correct statement about the use of an ICE table in equilibrium calculations?

Accepted Answer

It helps track the initial, change, and equilibrium concentrations of all species involved in a reaction.

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