Practice: For the reaction A → B, the rate constant is 0.0837 M–1•sec–1. How long would it take for [A] to decrease by 85%?
When we include the variable of time to our Rate Law then we obtain the Integrated Rate Laws.
Concept #1: Zero-Order Integrated Rate Law
Example #1: A plot of [NO3] vs time with a slope of 0.260 gives a straight line. What was the initial concentration of NO3 if after 35 seconds its concentration dropped to 2.75 x 10-2 M?
Concept #2: First-Order Integrated Rate Law
Example #2: A certain reaction has a rate constant of 0.289 s-1. How long (seconds) would it take for the concentration of reactant A to decrease from 1.43 M to 0.850 M?
Concept #3: Second-Order Integrated Rate Law
Example #3: The reactant concentration for a second-order reaction was 0.670 M after 300 s and 7.3 x 10-2 M after 750 s. What is the rate constant k for this reaction?
Practice: For the reaction A → B, the rate constant is 0.0837 M–1•sec–1. How long would it take for [A] to decrease by 85%?
Practice: The following reaction is known to be zero order in A with a rate constant of 3.7 × 10–3 M•s–1 at 25°C:
A → B + C
Calculate the concentration of C after 2.7 × 10–3 sec where [A]0 was 0.750 M at 25°C; assume [C]0 = 0 M.
Practice: For the decomposition of urea, NH2CONH2 (aq) + H+(aq) + 2 H2O (l) → 2 NH4+ (aq) + HCO3– (aq), the rate constant is 3.24 × 10–4 s–1 at 35°C. The initial concentration of urea is 2.89 mol/L. What fraction of urea has decomposed after 3.5 minutes?
Practice: Iodine-123 is used to study thyroid gland function. As this radioactive isotope breaks down, after 5.7 hrs the concentration of iodine-123 is 56.3% complete. Find the rate constant of this reaction.
