Rates and Rate Laws
What is the rate of reaction for reactant B in the following equation?
2A + 3B --> 4C + 2D
-1/3([B]/t)
What is the half-life of a reaction?
The amount of time it takes for a compound to reach half of its original value during a reaction.
Which step of a mechanism is the rate-determining step?
The slow step
If more of a reactant is added to a system, in which direction does the reaction shift to reestablish equilibrium?
Right -- towards the products
What is the only factor that influences the equilibrium constant?
Temperature
If reactant A is decreasing by 1.27 mol/L*s, at what rate is product C appearing?
2A + 3B --> 1C + 5D
0.635 mol/L*s
What is the purpose of a catalyst, and how do they achieve their goal?
To make the reaction go faster by decreasing the activation energy of the reaction.
If K > Q, in which direction does the reaction shift to reestablish equilibrium?
Right -- towards products
If the volume of the system below is increased, in which direction does the reaction shift to reestablish equilibrium?
Cl2(g) + I2(g) --> 2ICl(g)
Does not move at all -- equal amounts of moles on both sides
In an endothermic reaction, what is the sign of the H(rxn)?
It is positive.
Using the rate law below, determine what happens to the overall rate if [B] is doubled.
Rate = k[A][B]2
The overall rate quadruples (x4).
If a 1/[A] is plotted and provides a straight line with a constant slope, in what direction is the slope?
It is a positive slope -- second order.
Which states of matter can be included in the mass-action expression for any given reaction?
Gas and aqueous
When is using the simplifying assumption valid?
When 5% of the initial concentration (with an x variable subtracted from it) is larger than the x value itself.
True or false? Temperature is a catalyst.
False. Catalysts are generally enzymes.
For a reaction, the rate increases by a factor of nine when the concentration of NO is tripled while the concentration of H2 is kept constant. What is the order of the reaction with respect to NO?
Order of reaction with respect to NO is 2.
[NO]2
The rate law for a reaction is in first order with a rate constant of 2.13 mol/L*s. If the initial concentration of A is 0.594M, what is the half-life of the reaction?
0.325s
What are the intermediate(s) in the mechanism?
A --> 2B (fast)
B + C --> D + E (slow)
B + E --> F (fast)
B and E
Overall reaction: A + C --> D + F
Under which conditions would you expect to have the greatest net yield of product C?
A(g) + 2B(g) --> 3C(g) + D(g) H(rxn) = 85kJ/mol
High volume/low pressure, high temperature
Why are integrated rate laws useful?
They include time as a variable and can provide concentrations after a given amount of time.
Given experimental data (varying concentrations of reactants and their initial rates), explain how you would derive the overall rate law of a reaction.
(Decide if answer complies)
The concentration of a substance is reduced to 6.25% of its original value. How many half lives have taken place?
4 half-lives
For the reaction below, [A] = 2.15M, [B] = 0.585M, [C] = 0.8M, and [D] = 3.45M. The Kc value of this reaction is 3.5. What is the value of Qc? Is the reaction at equilibrium?
A(g) + 2B(g) --> 2C(g) + D(g)
Qc = 3.0
Not at equilibrium -- needs to shift to the right.
In an ICE table problem, you are provided the equilibrium concentration of a reactant. What can you then calculate, given that you completed an ICE table?
The x value, then can plug in all x values to solve for K/Q.
What is Dr. Hoober's PhD work in?
Grid-scale energy storage (those crazy batteries for energy instead of renewable resources)