Skip to main content
Ch.14 - Chemical Kinetics
Chapter 14, Problem 132

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?
Verified step by step guidance
1
Step 1: Determine the initial concentration of NO2. Since 0.0050 mol of NO2 is introduced into a 1.0 L flask, the initial concentration [NO2]_0 is 0.0050 M.
Step 2: Identify the order of the reaction. The problem involves the decomposition of NO2, which is often a second-order reaction. Verify this with the given data or assume second-order if not specified.
Step 3: Use the integrated rate law for a second-order reaction: \( \frac{1}{[A]} = kt + \frac{1}{[A]_0} \), where [A] is the concentration at time t, k is the rate constant, and [A]_0 is the initial concentration.
Step 4: Substitute the known values into the integrated rate law. Here, [A]_0 = 0.0050 M, [A] = 0.0010 M, and solve for time t. You will need the rate constant k, which should be provided or determined from additional data.
Step 5: Rearrange the equation to solve for t: \( t = \frac{1}{k} \left( \frac{1}{[A]} - \frac{1}{[A]_0} \right) \). Calculate t using the values from the previous steps.
Textbook Question
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.

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.