CHEM 2 CH 16 LS

Each reaction has its own characteristic reaction rate, which is determined by nature of the reacting species. However, reaction rate can be influenced by increasing the frequency and energy of the ___________ between molecules

collisions

Conditions that MUST be satisfied for a collision between reactants to be effective

-Appropriate molecular orientation -Enough energy to overcome Ea

Describe catalysts

-Catalysts provide a different mechanism for the reaction -Catalysts lower the activation energy of the rate-determining step in the reaction

Required for valid reaction mechanism

-Correlation of rate law with experimental rate law -Elementary steps sum to overall balanced equation -Physically reasonable elementary steps

Not required for valid reaction mechanism

-Unimolecular steps -Rate law includes intermediates

Transition theory focuses on the formation of the _______________ complex, which exists at the moment of highest _________________ energy in a reaction.

-activated -potential

In order to determine reaction orders experimentally, a series of experiments are run in which one reactant concentration _____________ while the other is kept _______________, and the effect on the initial rate is evaluated in each case.

-changes -constant

A reaction energy diagram plot potential ____________ versus reaction ___________

-energy -progress

Raising the temperature of a reaction increases the reaction rate by increasing the ____________ and ______________ of the collisions

-frequency -energy

The __________-____________ of a reaction is the time is the time required for the concentration to reach half its initial value.

-half -life

In general, a catalyst speeds up a given reaction by providing an alternative mechanism that has a ____________ activation energy, thus____________ the rate constant and the overall rate.

-lower -increasing

A reaction _____________ is a hypothesis about how a reaction occurs. This hypothesis is tested to see if it fits with the experimentally observed ______________ law.

-mechanism -rate

Collision frequency provides an upper limit on how fast a reaction can take place. The laws of probability tell us that the number of collisions depends on the ____________ of the number of reactant particles, not their _______________.

-product -sum

For any mechanism, only ___________ . involved up to and including the _____________ step appear in the overall rate law.

-reactants -slow

Steps of kinetics of a reaction

1. Gather experimental data consisting of a series of plots of concentration vs. time. 2. Determine the initial rates 3. Determine the reaction orders 4. Determine the rate constant (K) and the actual rate law.

Steps to determine reaction order from an integrated rate law

1. Rearrange each rate law into an equation for a straight line (y=mx+b) 2. Plot y vs. x for each integrated rate law. 3. The linear plot indicates the order of reaction.

An elementary step is characterized by its _______________, which is equal to the number of reactant particles in the step.

molecularity

Chemical kinetics studies the _____________ of chemical reactions, i.e. how fast reactants are converted into products.

rate

What are the most common types of heterogeneous catalysts?

solids

All other factors being equal, which of the following mixtures will have the fastest reaction rate?

An aqueous reactant mixed with another aqueous reactant with a stirring device. [The surface area of the reactants is maximized for this situation. The reactants are mixed and in the same phase]

Effect of reactant concentration on reaction rate

As reactant concentration increases, the number of reactant collisions increases, which in turn increases the reaction rate

Why does the rate of a reaction generally decrease over time?

As reactant is used up, there are fewer reactant particles to collide and therefore fewer effective collisions

What is an elementary step?

Each step that makes up a reaction mechanism

t1/2 does not depend on [reactant]initial

First-order reaction

The ________-_________ step in a reaction is the one that limits how fast the overall reaction proceeds

Rate-determining

t1/2 is inversely proportial to [reactant]initial

Second-order reaction

What is the molecularity of the elementary step A(g)+B(g)+C(g)= D(g)

Termolecular

The rate for an ELEMENTARY step can be deduced from its reaction stoichiometry [True or False]

True

What do the dashed lines represent in the illustration of the transition state of a reaction between BrCh3 and OH-?

The partial bonds forming and breaking in the reactants

t1/2 is directly proportional

Zero-order reaction

The _________ energy of a reaction is the energy threshold that colliding molecules must exceed in order to react

activation