CHAPTER 13 BASIC HOMEWORK
KINETICS I
For the reaction: 3BrO–(aq) –> BrO3–(aq) + 2Br–(aq) [BrO– ]initial is 0.60 M. 70 seconds later [BrO– ] is 0.12 M. What is the rate of change of [BrO– ] in M/s? (The brackets, [ ], indicate concentration, that is, molarity (M) or moles/liter.)
Notice that the rate of change of a reactant is negative because it is being used up.
Under a different set of conditions, the initial concentration of Br– is 0.00 M. 81 seconds later it is 0.82 M. What is the rate of change of Br– in M/s?
Notice that the rate of change of a product is positive because it is being produced.
Under a different set of conditions, the initial concentration of BrO3– is 0.23 M. 14 seconds later it is 0.83 M. What is the rate of change of BrO3– in M/s?
Notice that the rate of change of a product is positive because it is being produced.
Still for the reaction: 3BrO
–(aq) –> BrO
3–(aq) + 2Br
–(aq), what is the rate of reaction in M/s, if Δ[BrO
– ]/Δt = -0.074 M/s?
Help: Rate of reactionWe are given the rate of change of [BrO– ]. Because the chemical equation has 3 moles of BrO– , we must divide by 3 to get the rate of reaction.
Note that the rate of reaction is always positive.
Under a different set of conditions Δ[BrO3– ]/Δt = 0.029 M/s. What is the rate of reaction in M/s?
In this case, the coefficient of [BrO3–] is 1. Therefore:
Δ[BrO3– ]/Δt = Rate of reaction = .029
Note that the rate of reaction is always positive.
Under a different set of conditions Δ[Br– ]/Δt = 0.035 M/s. What is the rate of reaction in M/s?
Note that the rate of reaction is always positive.
Once again, take a look at the coefficients (molar amounts) in the chemical reaction to help you solve this one. If Δ[BrO3– ]/Δt = 0.010 M/s, then Δ[Br– ]/Δt = 0.010 x 2 = 0.020
If Δ[BrO3– ]/Δt = 0.024 M/s. What is [BrO– ]/Δt in M/s?
Note that [BrO– ]/Δt is negative, because BrO– is a reactant.
The rate of change of [B] is -0.243 M/min. What is the rate of reaction for the following reaction in M/min? 2A + 5B → 3C + 7D
Under a different set of conditions, the rate of change of [C] is 0.162 M/min. What is the rate of change of [D] in M/min? Hint given in feedback
Hint, if a = b and b = c, then a = c. Specifically, what is the rate of reaction using [C] and what is the rate using [D]? Set the rate using [C] = the rate using [D] and solve for the rate of change of [D].
If the rate of change of [C] is 0.149 M/min. What is the rate of change of [A] in M/s? Hint given in feedback’
Hint. What is the rate of reaction using [C] and what is the rate using [A]? Set the rate using [C] = the rate using [A] and solve for the rate of change of [A]. Check: is the rate of change of [A] positive or negative? Finally, units for rate of change of [A] are M/s not M/min. (1/min) = (1/min)(1 min/60 s).
To determine order of a particular reactant, look at its superscript. To determine overall reaction rate order, find the sum of superscripts.
Here we are essentially comparing the relative amount of change in concentration (∆[A]) to the relative amount of change in reaction rate in order to find the reaction order. Note that K (rate constant) cancels out in each equation.
Hint, what happens to the reaction rate when the reactant concentration is doubled?
What is k? Hint given in feedback
Substitute the data from one of the runs into the appropriate equation and solve for k. For zero-order, the rate of reaction = k[NO2]0 = k. For first-order, the rate of reaction = k[NO2]1 For one half-order, the rate of reaction = k[NO2]0.5 For second-order, the rate of reaction = k[NO2]2
What is the rate when [NO2] = 0.121 M? Hint given in feedback
Use the rate equation for the correct order with the k that you determined.
It is easiest to use the first and third run to determine the order.
What is k? Hint given in feedback
Substitute the data from one of the runs into the appropriate equation and solve for k. For zero-order, the rate of reaction = k[H2O2]0 = k. For first-order, the rate of reaction = k[H2O2]1 For one half-order, the rate of reaction = k[H2O2]0.5 For second-order, the rate of reaction = k[H2O2]2
What is the rate when [H2O2] = 0.082 M? Hint given in feedback
Use the rate equation for the correct order with the k that you determined.
For the reaction 2A(g) + 3B(g) → C(g) + 2D(g) the following experimental data was obtained for the rate:
Run | [A] (M) | [B] (M) | Rate (M/min) |
---|
1 | 0.01 | 0.2 | 2.2 |
2 | 0.01 | 0.4 | 4.4 |
3 | 0.02 | 0.4 | 8.8 |
The rate of reaction = kAxBy. What is x? Hint given in feedback
Hint: Notice that in run #2 and #3 the concentration of B does not change. So, it does not change the rate. Therefore, you can use these runs to find the order of the reaction with respect to A. In what two runs is the concentration of A the same? Use these runs to find the order of the reaction with respect to B. From run 2 to 3, [A] doubles. Rate also doubles. This means that x=1.
From run 1 to 2, [B] doubles. Rate also doubles. This means that y=1.
Plug in values for a single run, as well as the x and y values determined above to solve for k.
What is the rate when [A] = 0.043 M and [B] = 0.038 M? Hint given in feedback