Question 1

Rate Laws: How the Reaction Rate Depends on Concentration

Accepted Answer

The overall reaction rate can be expressed in terms of the rate of change of any component of the reaction. The rate law for a reaction is an equation relating the rate of production of products (or consumption of reactants) to the concentrations of starting materials.

Question 2

note

Accepted Answer

- The overall reaction rate can be expressed in terms of the rate of change of any component of the reaction. Since reactants are disappearing over the course of a reaction, the rate is expressed as negative for these components of the reaction. - For example, in the decomposition of dinitrogen pentoxide (N 2 O 5 ) to form nitrogen dioxide (NO 2 ) and oxygen (O 2 ), the rate of production of oxygen is equal to 1/4 the rate of production of nitrogen dioxide, and –1/2 the rate of disappearance of dinitrogen pentoxide. - The rate law for a reaction is an equation relating the rate of production of products to the concentrations of starting materials. - As an analogy, consider a junior high school dance. The rate of production of dancing couples is proportional to the number of non-dancing boys and girls at any given time. As couples form, and the number of non-dancing boys and girls decreases, the rate of production of dancing couples decreases. The rate law for this situation would be expressed as rate = k · [boys][girls], where k is the rate constant for this reaction. - In a general rate law, rate = k · [A] m [B] n , the constants m and n are the orders of the reaction. The reaction is said to be m the order with respect to A and nth order with respect to b. The reaction has an overall order of m + n. The values of m and n usually have no relation to the stoichiometric coefficients a and b—they must be determined experimentally.

Question 3

Chlorine gas(Cl2 ) reacts with fluorine gas (F2 ) according to the following equation. Cl2(g) + 3F2(g) → 2ClF3(g) Suppose you combine one mole of Cl2 with three moles of F2, and then made a graph of the concentration of the reactants and the products versus time. Which of the following statements would be true of the graph at time = t ?

Accepted Answer

The slope of the curve for ClF3 will equal twice the rate of the reaction.

Question 4

Dicyclopentadiene (C10H12 ) forms cyclopentadiene (C5H6 ) according to the following equation. C10H12 → 2C5H6 This reaction is first order overall, and the rate constant is equal to 1.92 × 10^−4 s^−1 at 170°C. What is the rate of formation of C5H6 when the concentration of C10H12 is 0.162 M?

Accepted Answer

6.22 × 10^−5 M / s

Question 5

The graph shows the concentrations of the reactants and products of a reaction over time. Based on this graph, which of the following conclusions can you draw about the reaction?

Accepted Answer

The reaction can be written as 2C + A → B

Question 6

Nitrogen dioxide (NO2 ) reacts with carbon monoxide (CO) according to the following equation. NO2(g) + CO(g) → NO(g) + CO2(g) If this reaction is second order in [ NO2 ] and second order overall, what are the units of k in the rate law of this reaction?

Accepted Answer

M ^−1s^−2

Question 7

Nitrogen dioxide (NO2 ) reacts with ozone(O3 ) according to the equation: 2NO2(g) + O3(g) → N2O5(g) + O2(g) If the rate law for this reaction is rate = k[ NO2 ] [O3 ], what is the overall order of the reaction?

Accepted Answer

second

Question 8

Borohydride ions (BH4− ) react with water according to the following equation. BH4− (aq) + 4H2O(l) → B(OH)4− (aq) + 4H2(g) The following graph shows the concentrations of the reactants and products of this reaction over time. Which curve best represents the concentration of B(OH)4−?

Accepted Answer

C

Question 9

Mercury(II) chloride (HgCl2 ) reacts with oxalate ions (C2O42− ) according to the following equation. 2HgCl2(aq) + C2O42− (aq) → 2Cl − (aq) + 2CO2(g) + Hg2Cl2(s) If Δ[CO2 ] / Δt = 5.2 × 10−7 M / s, what is the value of Δ[C2O42− ] / Δt at the same instant?

Accepted Answer

−2.6 × 10^−7 M / s

Question 10

Iodomethane reacts with hydroxide ions according to the following equation. CH3I(aq) + OH − → CH3OH(aq) + I − (aq) The dependence of the reactant concentration on the rate can be written as, Rate = k [CH3I] [OH − ]. What can you conclude about this reaction based on this information?

Accepted Answer

The reaction is second order overall.

Question 11

Suppose that the following reaction is first order in [B] and second order overall. 2A + B → 2C Which of the following equations represents the rate law for this reaction?

Accepted Answer

−d [B] / dt = k[A] [B]

Question 12

Disulfur dichloride (S2Cl2 ) reacts with carbon tetrachloride (CCl4 ) according to the following equation. S2Cl2(g) + CCl4(g) → CS2(g) + 3Cl2(g) This reaction is first order in [S2Cl2 ] and second order in [CCl4 ]. Which of the following changes would increase the initial rate of the reaction?

Accepted Answer

decreasing [S2Cl2 ] by a factor of 2 and doubling [CCl4 ]

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14.1.2 Rate Laws: How the Reaction Rate Depends on Concentration Flashcards

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