Chapter 14: Practice
For each of the following gas-phase reactions, indicate how the rate of disappearance of each reactant is related to the rate of appearance of each product: H2O2(g) = H2(g) + O2(g) N2(g) + 3H2(g) = 2NH3(g)
-Δ[H2O2]/Δt = Δ[H2]/Δt = Δ[O2]/Δt -Δ[N2]/Δt = -1/3Δ[H2]/Δt = 1/2Δ[NH3]/Δt rate of disappearance or appearance must be divided by the coefficient
Go to page 611, 14.9 Label the graph
1. Potential energy of reactants 2. Activation energy 3. change in energy (delta energy) 4. Potential energy of products
Time (min) 0 10 20 30 40 Moles of A 0.065 0.051 0.042 0.036 0.031 Between t = 10 min and t = 30 min, what is the average rate of appearance of B in units M/s? Volume of solution is 100 mL
1.3 x 10^-4 M/s
Consider the combustion of hydrogen 2 H2(g) + O2(g) = 2H2O (g). If the hydrogen is burning at the rate of 0.48 mol/s, what is the rate of consumption of oxygen? What is the rate of formation of water vapor?
O2 = .24 O2 H2O 0.48 mol/s
What is the reaction rate?
The change in the amount of reactant or product per unit time
What factors determine whether a collision between two molecules will lead to a chemical reaction? Does the rate constant for a reaction generally increase or decrease with an increase in reaction temperature? Which factor is most sensitive to changes in temperature - the frequency of collisions, the orientation factor or the fraction of molecules with energy greater than the activation energy?
The speed they are traveling (kinetic energy) and their orientation increase fraction of molecules with energy greater than activation energy
Reaction mechanism
a series of elementary reactions that describes how an overall reaction occurs and explains the experimentally determined rate law
Page 616 question 14.69 Answer questions using the graph
a. 2 b. 3 c. C to D d. ΔE +
The following mechanism has been proposed for the gas phase reaction of H2 with ICl: H2(g) + ICl(g) = HI(g) + HCl(g) HI(g) + ICl(g) = I2(g) + HCl(g) a. Write the balanced equation for the overall reaction. b. Identify any intermediates in the mechanism. c. If the first step is slow and the second one is fast, which rate law do you expect to be observed for the overall reaction?
a. H2(g) + 2ICl(g) = I2(g) + 2HCl (g) b. HI c. rate = k[H2][ICl]
A reaction A + B = C obeys the following rate law: Rate = k[B]^2 a. If [A] is doubled, how will the rate change? Will the rate constant change? b. What are the reaction orders for A and B? What is the overall reaction order? c. What are the units of the rate constant?
a. not change, either b. A = 0, b=2, OVERALL=2 c. M-1/s-1
What is the molecularity of each of the following elementary reactions? Write the rate law for each a. Cl2(g) = 2Cl(g) b. NO(g) + Cl2(g) = NOCl2(g)
a. rate = k[Cl2] unimolecular b. rate = k[NO][Cl2] bimolecular
Consider the gas-phase reaction between nitric oxide and bromine at 273°C 2NO(g)+Br2(g)→2NOBr(g)2NO(g)+Br2(g)→2NOBr(g). The following data for the initial rate of appearance of NOBr were obtained: Experiment [NO](M) [Br2](M) Initial Rate NOBr(M/s) 1 0.10 0.20 24 2 0.25 0.20 150 3 0.10 0.50 60 4 0.35 0.50 735 Part A Determine the rate law Part B Calculate the average value of the rate constant for the appearance of NOBr from the four data sets. Part C How is the rate of appearance of NOBr related to the rate of disappearance of Br2? Part D What is the rate of disappearance of Br2 when [NO]= 0.075 M and [Br2]= 0.25 M ?
a. rate = k[NO]^2[Br] b. k = 12000 M-2/s-1 c. 1/2 Δ[NOBr]/Δt = -Δ[Br2]/Δt d. 8.473 M/s
The iodide ion reacts with hypochlorite ion in the following way: OCl- + I- = OI- + Cl- Data of reaction: [OCl-] [I-] Initial Rate (M/s) 1.5x10-3 1.5x10-3 1.36x10-4 3.0x10-3 1.5x10-3 2.72x10-4 1.5x10-3 3.0x10-3 2.72x10-4 a. Write the rate law for this reaction b. Calculate the rate constant with proper units c. Calculate the rate when [OCl-] = 2.0 x 10-3 M and [I-] = 5.0 x 10-4 M
a. rate = k[OCl-][I-] b. 60.4 M-1/s-1 c. 6.04 x 10-5 M/s
Based on their activation energies and energy changes and assuming that all collision factors are the same, rank the following reactions from slowest to fastest. a. Ea = 45 kJ/mol; ΔE = -25 kJ/mol b. Ea = 35 kJ/mol; ΔE = -10 kJ/mol c. Ea = 55 kJ/mol; ΔE = 10 kJ/mol
c, a, b
The reaction 2NO(g) + Cl2(g) = 2 NOCl(g) is carried out in a closed vessel. If the partial pressure of NO is decreasing at the rate of 56 torr/min, what is the rate of change of the total pressure of the vessel?
decreases in pressure of the reactants results in the same increase of pressure in the products 28 torr/min 2NO(g) + Cl2(g) = 2 NOCl(g) -56 -28 +84 -1/2d[NO]/dt = - d[Cl2]/dt = 1/2d[NOCl]/dt
Is the rate of disappearance of reactants always the same as the rate of appearance of products?
no must use stoichiometry of reactants (moles of reactants/products) must be known to relate rate of disappearance to rate of appearance
