Concentration vs. Time Graphs

X → products

Pure substance X decomposes according to the equation above. Which of the following graphs indicates that the rate of decomposition is second order in X ?

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Tags

NGSS.HS-PS1-5

Consider the reaction represented by the equation 2 X + 2 Z → X₂Z₂. During a reaction in which a large excess of reactant X was present, the concentration of reactant Z was monitored over time. A plot of the natural logarithm of the concentration of Z versus time is shown in the figure above. The order of the reaction with respect to reactant Z is

• zero order

• first order

• second order

• third order

Tags

NGSS.HS-PS1-5

2 HO₂(g) → H₂O₂(g) + O₂(g)

The reaction represented by the chemical equation shown above occurs in Earth’s atmosphere. In an experiment, [HO₂] was monitored over time and the data plotted as shown in the following graph.

Based on the information, which of the following is the rate law expression for the reaction?

• rate = k

• rate = k[HO₂]

• rate = k[HO₂]²

• rate = k[HO₂][O₂]

Tags

NGSS.HS-PS1-5

H₂O₂ → H₂O+ ½ O₂

Hydrogen peroxide decomposes to produce water and oxygen according to the equation above. An experimentally determined graph for the first-order decomposition of hydrogen peroxide is provided below.

Which of the following best identifies the rate constant k

for the reaction based on the information in the plot of ln[H₂O₂] versus time (t)?

• k = ln[H₂O₂] at t = 0s

• k = ln[H₂O₂] at t = 500s

• k = −(slope of plot)

• k = −1/(slope of plot)

Tags

NGSS.HS-PS1-5

The rate constant (k) for the decay of the radioactive isotope I-131 is 3.6×10⁻³ hours⁻¹ . The slope of which of the following graphs is correct for the decay and could be used to confirm the value of k?

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2 H₂O₂(aq) → 2 H₂O(l) + O₂(g) ΔH° = −196 kJ/mol_rxn

The decomposition of H₂O₂(aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H₂O₂(aq) at a constant temperature of 300. K and recorded the concentration of H₂O₂ as a function of time. The results are given in the table below.

Which of the following statements is a correct interpretation of the data regarding how the order of the reaction can be determined?

• The reaction must be first order because there is only one reactant species.

• The reaction is first order if the plot of ln[H₂O₂] versus time is a straight line.

• The reaction is first order if the plot of 1/[H₂O₂] versus time is a straight line.

• The reaction is second order because 2 is the coefficient of H₂O₂ in the chemical equation.

2 N₂O₅(g) → 4 NO₂(g) + O₂(g)

A sample of N₂O₅ was placed in an evacuated container, and the reaction represented above occurred. The value of P_N2O5, the partial pressure of N₂O₅(g), was measured during the reaction and recorded in the table below.

Which of the following correctly describes the reaction?

• The decomposition of N₂O₅ is a zero-order reaction.

• The decomposition of N₂O₅ is a first-order reaction.

• The decomposition of N₂O₅ is a second-order reaction.

• The overall reaction order is 3.

Tags

NGSS.HS-PS1-5

A reaction was observed for 20 days and the percentage of the reactant remaining after each day was recorded in the table above. Which of the following best describes the order and the half-life of the reaction?

• First order; half-life is 3 days

• First order; half-life is 10 days

• Second order; half-life is 3 days

• Second order; half-life is 3 days

• Second order; half-life is 10 days

Tags

NGSS.HS-PS1-5

The graph above shows the results of a study of the reaction of X with a large excess of Y to yield Z. The concentrations of X and Y were measured over a period of time. According to the results, which of the following can be concluded about the rate law for the reaction under the conditions studied?

• It is zero order in [X].

• It is first order in [X].

• It is second order in [X].

• It is first order in [Y].

• The overall order of the reaction is 2.

Tags

NGSS.HS-PS1-5