Chapter 14 Kinetics

A reaction A+B⟶C obeys the following rate law: Rate=k[B]2. What is the reaction order for A?

0

A reaction A+B⟶C obeys the following rate law: Rate=k[B]2. What is the reaction order for B?

2

For the elementary reaction NO3 + CO → NO2 + CO2 the molecularity of the reaction is ________, and the rate law is rate = ________.

2, k[NO3][CO]

Which substance in the reaction below either appears or disappears the fastest? 4NH3 + 7O2 → 4NO2 + 6H2O

7O2

What is the difference between a homogeneous and a heterogeneous catalyst?

A homogeneous catalyst is present in the same phase as the reactants in a reaction mixture. A heterogeneous catalyst exists in a phase different from the phase of the reactant molecules, usually as a solid in contact with either gaseous reactants or reactants in a liquid solution.

What is meant by the term rate-determining step?

A rate-determining step is the slowest step in a reaction mechanism. It limits the overall reaction rate.

What is a reaction mechanism?

A reaction mechanism is a series of elementary reactions that describe how an overall reaction occurs and explain the experimentally determined rate law.

A reaction A+B⟶C obeys the following rate law: Rate=k[B]2. What are the units of the rate constant?

M-1s-1

A reaction A+B⟶C obeys the following rate law: Rate=k[B]2. Will the rate constant change?

No

Two reactions have identical values for Ea. Does this ensure that they will have the same rate constant if run at the same temperature?

No, this does not ensure that they will have the same rate constant if run at the same temperature because the rate constant depends on concentration [A], temperature, and Ea. The effectiveness for collisions is also different in each reaction.

Two similar reactions have the same rate constant at 25∘C, but at 35∘C one of the reactions has a higher rate constant than the other. Account for these observations.

The rate constant depends on more than just temperature. It also accounts for activation energy and concentration. The rate constant at 35 degrees C would have a lower activation energy because its energy increase is used more effectively.

In a reaction involving reactants in the gas state, how does increasing the partial pressures of the gases affect the reaction rate?

The rate will increase

A reaction A+B⟶C obeys the following rate law: Rate=k[B]2. If [A] is doubled, how will the rate change?

The rate would remain the same.

Rate constant does not depends on

concentration of reactants, concentrations of products, and identity of the reactants

In general, as activation energy increases, reaction rate

goes down regardless of whether the reaction is exothermic or endothermic

In general, as temperature goes up, reaction rate

goes up regardless of whether the reaction is exothermic or endothermic

A reaction was found to be third order in A. Increasing the concentration of A by a factor of 3 will cause the reaction rate to

increase by a factor of 27

Rate constant depends on

magnitude of Ea and reaction temperature

A unimolecular elementary reaction involves _____________ ; the activated complex is derived from _____________. A bimolecular elementary reaction involves ______________; the activated complex is derived from ________________.

only one reactant molecule; a single molecule; two reactant molecules; the overall process

A burning splint will burn more vigorously in pure oxygen than in air because

oxygen is a reactant in combustion and concentration of oxygen is higher in pure oxygen than is in air

An elementary reaction is a ___________, that occurs _________________; the order is given by the ______________ in the balanced equation for the reaction

process, in a single event, coefficients

What is a catalyst?

substance that changes the speed of a chemical reaction without undergoing a permanent chemical change itself.

What is the molecularity of an elementary step, given its rate law is as follows: Rate = k[A]2[B]?

termolecular

Do catalysts affect the overall enthalpy change for a reaction, the activation energy, or both?

the activation energy

You perform a series of experiments for the reaction A→B+C and find that the rate law has the form rate = k[A]x. There is no rate change when [A] is tripled.

x=0

You perform a series of experiments for the reaction A→B+C and find that the rate law has the form rate = k[A]x. The rate increases by a factor of 9 when [A] is tripled.

x=2

You perform a series of experiments for the reaction A→B+C and find that the rate law has the form rate = k[A]x. When [A] is doubled, the rate increases by a factor of 8.

x=3