Unit 5 Thou Shalt Not Forget, AP Chemistry

Increasing concentration leads to

faster rate of reaction

Increasing temperature

increases reaction rate

Catalyst

substance that speeds up the rate of a chemical reaction while remaining chemically unchanged

[Reactants] against time

straight line = shows zero order

[Reactants] against time First Order

Constant Half life

[Reactants] against time Second Order

Not constant Half life

Rate against [reactants] zero order

rate independent of concentration of reactants

First order

rate directly proportional

Second order

Rate varies to greater degree

The overall rate of a complex chemical reaction is only dependent upon

slowest stage

Collision theory says that a reaction will only take place if:

1. Reactants come into contact

2. The activation energy is met

3. The collision has the right orientation

Greater concentration means...

Faster rate of reaction

Increased temperature means...

Faster rate of reaction

If a solid is broken up into smaller pieces, the rate of reaction increases. Why?

The surface area increases

Addition of a catalyst does what?

Provides an alternate pathway (for the reaction to take place) that requires a lower activation energy

K

rate constant

In the rate law, x, y, and z are

the reaction orders

Only the reactants in the __________ step will be included in the rate law

slow, rate- determining

If a substance is present at the beginning of a reaction and present in the same form at the end of a reaction, it can be identified as a...

catalyst

To determine the order of a reaction from a graph, look for the graph with a

Straight line (constant slope)

rise in temperature

increase rate of reaction

increase concentration

increase collision frequency

catalyst

substance that speeds up the rate of a chemical reaction

enzyme

speeds up chemical reactions while lower activation energy

catalyst

provide a alternative pathway with a lower Eact.

K

equilibrium constant

Which step would included the reactants of the rate law?

slow, rate-determining

zero order

1st order

2nd order

Activation Energy

Energy needed to get a reaction started

Unimolecular reactions

reactions in which a single chemical species decomposes or rearranges

Bimolecular reactions

chemical reactions that involve the collision of two chemical species

Trimolecular reactions

when three reactants collide to form new products: third order

First Order

rate=k[A]

In [A]t versus t

Second Order

Rate=k[A]^2

1/[A]t versus t

Catalysts

substances that speed up chemical reactions

Rise in temperature =

Increased rate of reaction (more particles have minimum energy needed)

Greater concentration =

Greater frequency of collisions and greater chance of success

Arrhenius equation

relates rate constants, activation energy, and temperature

Rate

Change in concentration of a substance/ change in time

Reaction Mechanisms

Series of steps by which a reaction occurs

Intermediate

a species that is neither a reactant nor a product but that is formed and consumed in the reaction sequence

molecularity

the number of species that must collide to produce the reaction indicated by that step

rate determining step

the slowest step in a reaction mechanism

A chemical eqaution

only tells us what reactants become products

What is K

rate constant

What is E

activation energy

What is R

universal gas constant

Remember to measure temperature

in kelvins

reactions must _______ in the correct _______ in order to occur

collide, orientation

________ must be met for reaction to occur

activation energy

Increasing reactant concentration

generally increases reaction rate

higher temperature has _______ arrows in a heat diagram

longer

higher temperatures cause molecules to move ________

faster

2 systems come together and energy moves from the _____ to the _____ one

hot to cold

exothermic

Releases heat

endothermic

Absorbs heat

negative delta H

exothermic

First electron affinity

The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

one

The rate of a reaction can be determined by the decreased concentration of the reactants and the increased concentration of the products

two

Collision theory tells that a reaction will only take place if the reactants collide with enough activation energy and at the right angle

three

elementary steps can have 1,2, or 3 species collide and react to form products. That being said, the fewer molecules involved in the elementary reaction, the more likely it is that one of the collisions will be in the correct orientation

four

Factors that can influence the rate of a chemical reaction are concentrations, temperature, solid particle size, and catalysts. Solid particle size matters because of surface area. The smaller the particles, the greater the surface area, and more particles can collide, increasing the rate of the reaction. Catalysts lower the activation energy, which allows more particles to meet that energy and collide more. This speeds up the rate of the reaction. With concentration, the more you have of something, the more particles you have, the more Collisions you will have. Temperature affects the rate by causing the kinetic energy of the particles to go up, making the particles move faster and make more collisions.

five

The overall rate of a chemical reaction is based on the slowest elementary step

six

Intermediates are created in one elementary step then used up in the following elementary step

seven

First order graphs show a constant half life. Second order graphs might look like they have a constant half life, but they don't.

eight

The order with respect to a given reactant is the power to which the concentration of that reactant is raised to the rate equation

nine

Catalyst are present at the beginning of the reaction and the end of the reaction in its same form

ten

A reaction that has no effect on the rate is said to have an order equal to zero

Minimum Energy

Activation Energy

Reactants

must collide at the correct orientation for the reaction to occur

Elementary Steps

form substances in a single step

The more molecules there are

the chances for correctly oriented collisions decreases

Increased Concentration

causes greater frequency of collisions and greater chances of successful collisions

Intermediates

are not apart of the product

Increase in temperature

results in increased rate of reaction

Catalysts

are present in the product

Zero Order

1st Order

2nd Order

Rate = k

Rate = ln[A]

Rate = 1/[A]

If the constant increases

the rate increases

the _______ determines the rate

slow step

What do catalysts affect?

Only the activation energy

bimolecular

two reactants form products

intermediate substance

formed in one step of reaction then used in subsequent reaction

Activation Energy

Energy needed to get a reaction started

First Order

rate=k[A]In [A]t versus t

Second Order

Rate=k[A]^2 1/[A]t versus t

Arrhenius equation

relates rate constants, activation energy, and temperature

Catalysts

substances that speed up chemical reactions

Greater concentration

Greater frequency of collisions and greater chance of success

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.

few molecules in the elementary reaction

the more likely it is that one of the collisions will be in the correct orientation

increase of molecularity

causes the chance of correct oriented collisions to decrease

an increase of reaction concentration

causes a greater frequency of collision

Increase in temperature

causes increase in the reaction rate

Addition of a catalyst

a substance that increases the rate of a chemical reaction by lowering its activation energy. The catalyst may participate as a reactant but it is then regenerated as a product and is thus available to catalyze subsequent reactions. It also decreases the activation energy

Delta H (∆H)

remains the same in the presences and absence of a catalyst in a reaction

The overall rate of a complex chemical reaction is only dependent upon

the slowest elementary step

Rate= k[A]^x[B]^y[C]^z

k= rate constant

x,y,z= orders with respect to the concentrations

ABC= concentrations

Rate laws

it is possible to deduce anything about the order of a reaction from the stoichiometry of the balanced equation that describes the complete, complex, chemical reaction