Chemical Kinetics Flashcards
(HIGH YIELD) Reactions can be spontaneous or nonspontaneous. What quantitative measurement determines whether or not a reaction will occur by itself without additional input of energy?
Gibbs free energy (delta G)
(HIGH YIELD) Many reactions proceed by more than one step, the series of which is known as the ______ of a reaction.
Mechanism
(HIGH YIELD) The slowest step in any proposed mechanism is called the _____ _____ step because it acts like a kinetic bottleneck, preventing the overall reaction from proceeding any faster than that slowest step.
Rate-determining
(HIGH YIELD) For a reaction to occur, molecules must collide with each other. The _____ theory of chemical kinetics states that the rate of a reaction is proportional to the number of collisions per second between the reacting molecules.
Collision
(HIGH YIELD) The minimum energy of collision necessary for a reaction to take place is called the _____ _____.
Activation energy (E sub a)
(HIGH YIELD) The rate of a chemical reaction can be expressed with what equation? (Hint: rate = ___ x ___)
Rate = Z x f, where Z is the total number of collisions occurring per second and f is the fraction of collisions that are effective.
(HIGH YIELD) The energy required to reach the transition state is ______ ______.
Activation energy
(HIGH YIELD) What is the name of the difference between the free energy of the products and the free energy of the reactants?
The free energy change of the reaction (delta G of the reaction)
(HIGH YIELD) A NEGATIVE free energy change indicates what type of reaction?
Exergonic (energy is given off)
(HIGH YIELD) A POSITIVE free energy change indicates what type of reaction?
Endergonic (energy is absorbed)
(HIGH YIELD) List some factors that can INCREASE the rate of a reaction.
- Increasing reaction concentrations (for all but zero-order reactions)
- Increasing temperature (exception: catalysts may denature if the temperature is too high, causing the reaction rate to plummet)
- Choosing a specific reaction medium (some molecules are more likely to react in aqueous environments, while others are not)
- Adding a catalyst
(HIGH YIELD) In ______ catalysis, the catalyst is in the same phase (solid, liquid, gas) as the reactants. In ______ catalysis, the catalyst is in a distinct phase.
Homogeneous; heterogeneous
(HIGH YIELD) True or false: Catalysts change only the rates of reactions and do not impact the free energies of the reactants or the products.
True. Catalysts change the forward rate and reverse rate by the same factor.
For nearly all forward, irreversible reactions, the rate is proportional to the concentrations of the reactants, with each concentration raised to some exponent. How is this exponent determined?
The exponent can only be determined experimentally. It is NOT determined by the stoichiometric coefficient for the relevant reactant.
Give an expression for the rate law of a chemical reaction with only two reactants, A and B.
rate = k[A]^x[B]^y
where k is the rate constant and the overall order of the reaction is the sum of x and y
True or false: PRODUCT concentrations never appear in a rate law.
True. Only the concentrations of REACTANTS are relevant in a rate law.
A ____ ____ reaction is one in which the rate of formation of product is independent of changes in concentrations of any of the reactants.
Zero-order. These reactions have a constant reaction rate equal to the rate constant, k, which has units of M/s.
What are two ways to increase the rate of a zero-order reaction?
- Raise the temperature (remember that k is temperature-dependent)
- Add a catalyst
Plotting a zero-order reaction on a concentration vs. time curve results in what type of graph?
Linear, with a negative slope where k = -slope
A ____ ____ reaction has a rate that is directly proportional to only one reactant, such that doubling the concentration of that reactant results in a doubling of the rate of formation of product.
First-order, where k has units of s^-1
Plotting a first-order reaction on a concentration vs. time curve results in what type of graph?
Nonlinear. If the natural log of the concentration (ln[A]) is plotted vs time, the graph will be linear with a negative slope.
A ____ ____ reaction has a rate that is proportional to either the concentrations of two reactants or to the square of the concentration of a single reactant.
Second-order, where k has units of M^-1 s^-1
What type of reaction refers to non-integer orders (fractions) or, in other cases, to a reaction with rate orders that vary over the course of the reaction?
Mixed-order reaction
What name is given to reactions whose orders are fractions rather than integers?
Broken-order reactions
