CH 112- Chapter 15: Chemical Kinectics

Chemical Kinetics

The study of reaction rates and reaction mechanisms

Reaction Mechanisms

Describes the molecular events from reactant to product

Reaction Rate

The speed of a reaction

What is the Equation for reaction rate?

Rate = Change in Molarity/ Change in Time

Higher concentrations increase what?

rates

Rate comparisons depend on what?

molar relationships

In differential Rate law, the reaction rate depends on what?

Reactant concentrations, not their volume.

The number of molecules determines what?

reaction rate

What is the differential rate law equation?

k \[A\]^m \[B\]^n

Sensitivity measurements relate what?

the rate to reactant concentrations

m = 1:

direct relation

m = 2:

square relation

m = 0:

no relation

m < 0:

inverse relation

What rate law equation describes the net factor effect on the rate for each concentration?

Rate = k \[A\]^2 \[B\] \[C\]^-1

What is determined by exponents

the reaction order

What are single reactants ordered by?

m or n

How are integrated rate laws developed?

From integrating rate relationships and measuring the change in concentration with time. Unique to each reaction order.

What kind of form is integrated rate law presented in?

slope-intercept form: y=mx+b

What is the half-life of integrated rate law?

The time required for half a reactant concentration to react

What are the types of reaction order

zero order, first order, and second order

What is the differential rate law for zero order?

Rate = k

What is the integrated rate law for zero order?

\[A\]t = -kt + \[A\]0

What is the successive half-life of zero order __halved__ to?

t1/2 = \[A\]0 / 2k

What is the differential rate law for the first order?

Rate = k \[A\]

What is the integrated rate law for the first order?

ln \[A\]t = -kt + ln \[A\]0

What is the first-order half-life __equal__ to?

t1/2 = ln2 / k

What is the differential rate law for the second order?

Rate = k\[A\]^2

What is the integrated rate law for the second order?

1/\[A\]t = kt + 1/\[A\]0

What is the successive half-life of the second order __doubled__ to?

t1/2 = 1/k\[A\]0

What determines a reaction order of a graph

A straight line through the data

What is activation energy?

How much energy required to start a reaction

To start an activation energy reaction, what must happen?

Every mixture must absorb energy from the Ea

What does the reactant’s energy exchange depend on?

on the products and reactants: dHrxn = Hp - Hr

What is the formula for __exothermic__?

dHrxn < 0

What is the formula for __endothermic__?

dHrxn > 0

What do catalyst reduce?

They decrease activation energy (not dHrxn) with no net change.

What is adsorption?

The catalyst dissociates and weakly reacts with reactants

What is diffusion?

The reactants spread across the catalyst and react with each other at its surface.

What is desorption?

The products depart the catalyst, and the catalyst returns to neutral. (original state)

What are the general types of a catalyst?

Homogeneous and Heterogeneous

What is a homogeneous catalyst?

The catalyst and reactants are in the same phase

What is a heterogeneous catalyst?

The catalyst is solid, but the reactants are fluid.

What is an elementary reaction

A single “molecular event” in the reaction.

What is the sum of elementary reactions?

the overall reaction

What is molecularity?

The number of molecules involved in an elementary reaction

What are the types of molecularity?

unimolecular, bimolecular, and termolecular

What is unimolecular?

One molecule decomposes or changes electric potential

What is bimolecular?

Two molecules collide to react. (Most common, but as double

replacement)

What is termolecular

Three molecules collide to react. (Often occurs as two bimolecular reactions)

How are overall reaction rate laws determined?

experimentally

What are elementary reactions rate laws based on?

on molecularity

What is the coefficient in an elementary reaction?

It is the experiment’s exponent in __its own__ rate law

What is the slowest elementary reaction called?

rate-determining step

What kind of reactants reacts the fastest?

Fluid reactants

What are fluid molecules?

They have the most energy and they mix towards completion.