ap chem unit 5

rate law

an expression relating the rate of a reaction to the concentration of the reactants

order of reactant

The power to which the reactant's concentration is raised in the rate-law expression.

overall reaction order

the sum of all the exponents in a rate law expression

rate constant

a constant of proportionality between the reaction rate and the concentrations of reactants that appear in the rate law (ie a constant created to hide the other factors that impact reaction rate, such as temperature)

0th order reaction

Reaction rate is independent of the [reactant];

2x [reactant] --> no change in rxn rate

1st order reaction

Reaction rate is directly proportional to concentration of reactant [R];

2x [R] --> reaction rate doubles

rate=k[A]

2nd order reaction

The concentration of a reactant is raised to the second power. If the concentration doubles, the rate is multiplied by 4. If the concentration is tripled, the rate increases 9x

rate law equation

rate = k [A]^x [B]^y

half-life

The time required for one half of the atoms of a radioisotope sample to decay

Half life and rate of decay

t 1/2 = 0.693/k

elementary reaction

a single step in a reaction mechanism; describes an individual molecular event

reaction mechanism

the step-by-step sequence of reactions by which the overall chemical change occurs

reaction intermediate

temporary substance formed and consumed in a chemical reaction; also known as a transition state

unimolecular reaction

an elementary reaction that involves a single molecule

bimolecular reaction

An elementary reaction involving the collision of two reactant species

termolecular reaction

elementary reaction involving the simultaneous collision and combination of three reactant species - this is very unlikely

collision theory

For a reaction to occur, the particles must collide, they must collide with the appropriate orientation, and they must collide with sufficient energy.

Maxwell-Boltzmann distribution

The distribution of energies (and therefore speeds) of the molecules in a gas or liquid.

kinetic energy

the energy an atom/molecule has due to its motion

reaction energy profile

A graph showing the relative energies of the reactants and products in a chemical reaction, with the horizontal axis representing the progress of the reaction and the vertical axis representing the energy of the reaction

activated complex (transition state)

the arrangement of atoms found at the top of the potential energy barrier as a reaction proceeds from reactants to products

reaction coordinate

A visual representation of a chemical reaction and the accompanying energy changes (ie the progress of a reaction)

activation energy (Ea)

the minimum amount of energy required to initiate a chemical reaction

catalyst

substance that increases reaction rate by stabilizing transition state, decreasing the activation energy

How does a catalyst work?

1. Forms more stable activated complex

2. Increases number of molecular collisions

3. Improves molecular orientations

elementary steps (elementary reactions)

proposed steps where particles actually collide

rate-determining step

the overall reaction cannot occur faster than the slowest reaction in the mechanism

equilibrium

state where rate of forward reaction is equivalent to rate of reverse reaction

homogeneous catalysis

A reaction in which the catalyst and reactants are in the same physical state (ie reactants in the elephant's toothpaste demo are liquids + liquid catalyst)

heterogeneous catalyst

A catalyst in a different phase from the reactants.

adsorption

The process of binding or sticking to a surface.

desorption

Release of an adsorbed substance from a surface

steady state approximation

can be used when the differential rate law for an intermediate is equal to zero...Means the change of concentration of a species is zero, which happens if the intermediate is consumed as quickly as it is formed

0th order reaction

1st order reaction

2nd order reaction

Multi-step reaction profile