Ch.14 - Chemical Kinetics

Problem 134

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Chapter 14, Problem 134

The following experimental data were obtained in a study of the reaction 2 HI1g2S H21g2 + I21g2. Predict the concentration of HI that would give a rate of 1.0 * 10-5 M>s at 650 K.

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Step 1: Identify the rate law for the reaction. The general form of the rate law is rate = k[HI]^n, where k is the rate constant and n is the order of the reaction with respect to HI.

Step 2: Use the data from experiments 1 and 2 to determine the order of the reaction (n). Compare the rates and concentrations to find the relationship between them.

Step 3: Calculate the rate constant (k) using the data from one of the experiments (e.g., experiment 1). Use the rate law and the known concentration and rate to solve for k.

Step 4: Use the rate law and the calculated rate constant (k) to predict the concentration of HI that would give a rate of 1.0 * 10^-5 M/s at 650 K.

Step 5: Solve for the concentration of HI by rearranging the rate law equation to isolate [HI] and substituting the given rate and calculated rate constant.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Rate of Reaction

The rate of reaction refers to the speed at which reactants are converted into products in a chemical reaction. It is typically expressed in terms of concentration change over time, such as moles per liter per second (M/s). Understanding how concentration affects the rate is crucial, as higher concentrations of reactants generally lead to increased reaction rates due to more frequent collisions between molecules.

Temperature and Reaction Rate

Temperature plays a significant role in influencing the rate of chemical reactions. As temperature increases, the kinetic energy of molecules also increases, leading to more frequent and energetic collisions. This often results in a higher reaction rate. The Arrhenius equation quantitatively describes this relationship, showing how temperature affects the rate constant of a reaction.

Concentration and Rate Law

The rate law expresses the relationship between the rate of a chemical reaction and the concentration of its reactants. It is typically formulated as rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the orders of the reaction with respect to reactants A and B. By analyzing experimental data, one can determine the order of the reaction and predict how changes in concentration will affect the reaction rate.

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Textbook Question

The reaction 2 NO1g2 + O21g2S 2 NO21g2 has the thirdorder rate law rate = k3NO423O24, where k = 25 M-2 s-1. Under the condition that 3NO4 = 2 3O24, the integrated rate law is 13O242 = 8 kt +113O24022 What are the concentrations of NO, O2, and NO2 after 100.0 s if the initial concentrations are 3NO4 = 0.0200 M and 3O24 = 0.0100 M?

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Open Question

Consider the following data for the gas-phase decomposition of NO2: 2 NO2(g) → 2 NO(g) + O2(g) If 0.0050 mol of NO2 is introduced into a 1.0 L flask and allowed to decompose at 650 K, how many seconds does it take for the NO2 concentration to drop to 0.0010 M?

Open Question

Use the following initial rate data to determine the activation energy (in kJ/mol) for the reaction A + B ⇌ C.

Open Question

The reaction AS C is first order in the reactant A and is known to go to completion. The product C is colored and absorbs light strongly at 550 nm, while the reactant and intermediates are colorless. A solution of A was prepared, and the absorbance of C at 550 nm was measured as a function of time. (Note that the absorbance of C is directly proportional to its concentration.) Use the following data to determine the half-life of the reaction.

Textbook Question

Values of E_a = 6.3 kJ/mol and A = 6.0⨉10⁸/(M s) have been measured for the bimolecular reaction: NO(g) + F₂(g) → NOF(g) + F(g) (a) Calculate the rate constant at 25 °C.

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Textbook Question

Values of E_a = 6.3 kJ/mol and A = 6.0⨉10⁸/(M s) have been measured for the bimolecular reaction: NO(g) + F₂(g) → NOF(g) + F(g) (d) Why does the reaction have such a low activation energy?

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