Chem

Chemical kinetics

The study of reaction rates (speed of reaction)

Factors that influence the reaction rate

1. concentration of reactants

2. nature of the reaction (amount of activation energy)

3. temperature

4. reaction mechanism

5. presence of catalyst

Collision Theory

1. reactions occur when there are collisions between reactants

2. BUT not all collisions lead to a reaction

- molecules must be properly oriented (collision geometry)

- only molecules with enough kinetic energy (KE) to break the bonds will result in a reaction

- molecules with low KE (KE < Ea) will bounce off each other

Activation Energy (Ea)

1. always positive

2. depends on the nature of reaction (low Ea= fast; high Ea = slow)

3. independent of concentration/temperature

activated complex

intermediate between reactants and products (psuedo-molecule)

catalyst

lowers activation energy without being consumed in the reaction

reaction rate

a positive quantity that expresses how the concentration (Molarity) of a reactant or product changes with time

reaction rate & temperature

as temperature increases, rate increases (in general)

reversible reactions

reactions that do not go to completion

equilibrium system

the forward and reverse reactions occur at the same rate (speed) and the concentration of reactants and products remain constant

equilibrium is a dynamic process

at equilibrium the forward and reverse reactions are still occuring (dynamic), even though the concentrations remain constant

Stresses alter equilibrium

When a system is at equilibrium, it will stay that way until something changes this condition

Pressure effects on equilibrium

when pressure is increased, the stress is relieved by favoring the reaction with fewer gas molecules (fewer gas molecules = lower pressure)

Stresses on equilibrium

1. temperature

2. concentration

3. pressure

Le Chatelier's Principle

When a system at equilibrium is disturbed by applying a stress, a new equilibrium position is attained to relieve the stress

equilibrium constant

the ratio of product concentration to the reactant concentration at equilibrium (no units)

Meaning of equilibrium constant

∙ Keq > 1: products are favored (forward reaction)

∙ Keq < 1: reactants are favored (reverse reaction)

The Haber-Bosch Process

The process of "fixing" nitrogen from the atmosphere in the form of ammonia

Exothermic Reaction (graph)

- fast because of low Ea

- change in temperature is negative

- releases energy

Endothermic Reaction (graph)

- slow because it needs a lot of Ea

- change in temperature is positive

- absorbs energy

branch of chemistry concerned with reaction rates and reaction mechanisms

kinetics

states that in order for a reaction to occur, the reactants must collide with one another with a sufficient amount of kinetic energy, as well as the correct orientation in space in order for them to combine

collision theory

successful collision

effective collision

factors that affect the collision of reactants

nature, concentration, surface area(solids), pressure (gases), temperature, catalysts

bond type affects the...of reactants

reaction rate

reacts faster than molecular reactants, as the particles within water are separated and therefore more accessible, and ionic bonds typically have fewer bonds to rearrange

aqueous ionic solutions

dependent on the amount of particles within the substance

concentration

greater concentration results in...

increased collision rates

in solids, a greater amount of exposed surface area will result in__________, as a greater amount of a substance exposed will result in a greater amount base to collide off of

increased collision rates

temperature's correlation with collission

increased temperature results in high collision rates

pressure's correlation with collission

increased pressure (in gases only) results in higher collission rates

temperatures correlation with collision with gases

increased temperature in gases results in lower rates of collision

reduce the activation energy required for a reaction to occur, without sacrificing any other components

ex:) flint, matches, etc

catalyst

the amount of energy absorbed or released during a chemical reaction

enthalpy

bond forming reactions, energy is released as a product of the reaction; in this type of reaction, the potential energy of the products is less than that of the reactants, as excess energy is leaving the reaction as a product; features a negative change of heat on the reference teable

exothermic reactions

energy will appear on the right side in this type of reaction

exothermic

bond breaking reactions; in this reaction, heat is absorbed, as energy is required to join the reactants together; the potential heat of the products is greater than that of the potential heat of the reactants; features a positive change of heat on the reference table

endothermic reactions

energy will appear on the left side of this reaction

endothermic reactions

change of heat on the reference table

Table I

occurs in most reactions

both endothermic and exothermic reactions

the potential energy of the products will appear higher in this graph, as heat is aborbed into the products

endothermic reactions

the potential energy of the products will appear lower in this graph, as heat is released by the reactants into the products

exothermic reactions

the minimum amount of energy that colliding particles must have in order to react

activation energy

point at which the reaction has reached is maximum potential energy, and has reached the required amount of energy for the reaction to begin; following this point, the reaction may begin

activation complex

lowers the activation energy by finding an alternate reaction pathway/mechanism; it doesn't alter anything, and any stored energy isn't used up

catalyst

featured within reactions when the rated of forward and reverse reactions are equal; reversible chemical reaction (has the ability to both synthesize and decompose)

equilibrium reactions

must remain constant within reactions at equilibrium

concentrations (amounts of particles)

requires a closed system, or controlled environment for this to occur; meaning no reactant, product, or means of energy may escape, for the reaction to occur

equilibrium reactions

forms of stress that may alter an equilibrium reaction

changes in temperature, pressure, or concentration

what are the two brands of equilibrium

chemical equilibrium and physical equilibrium

physical equilibrium that exists between two phases of matter; the substance remains the same, with just the phase of the substance altering between

ex:) water at its melting and freezing points;will remain in both the solid and liquid phases

phase equillibirum

physical equilibrium which exists only in saturated solutions; the rate of dissolving is equal to the rate of recrystallization; will fluctuate between hat of a solid and aqueous state, with the substance itself remaining chemically identical to the other

solution equilibrium

equilibrium reaction in which a chemically distinct product is produced from two separate reactants

chemical equilibrium

within a chemical reaction, a ____________ and __________ cannot exist, as they both result in a loss of product

insoluble solid in an aqueous solution, uncontained gas

when a system at equilibrium is subjected to a stress, the system will shift to the left or right in order to relieve the stress, thus creating a new equilibrium

Chatelier's principle

shift to right

forward shift

shift to left

reverse shift

indicates molar concentration

brackets

as a result of excess molecular amounts, either more reactants or products will be produced within an equilibrium reaction

increase in concentration

no shift permitted despite pressure changes

identical amounts of particles on each side

decreases the time needed to reach equilibrium

catalyst

once at equilibrium, the catalyst increases both forward and backward reaction time.....

equally

naturally occurring reactions; typically favor the formation of products and exothermic reactions; favors simpler products in greater quantities

spontaneous reactions

features a low enthalpy (exothermic reactions) and a high entropy (chaos)

spontaneous reactions

low enthalpy and high entropy

always spontaneous

high enthalpy and low entropy

never spontaneous

low enthalpy and low entropy

dependent on temperature

high enthalpy and high entropy

dependent on temperature

kinetics

study of how fast a chemical reaction is occurring and describes the rate of change in the concentrations of the reactants and products over time in chemical rxn

collision theory

reaction is most likely to occur if the reactant particles collide with sufficient energy and proper orientation

Factor that affect rate of reaction:

Temperature

temp increases, rate of chemical rxn increases

higher temps=particles collisions more frequently and with more energy

Factor that affect rate of reaction:

Surface Area

surface area increase=rate of rxn increase

Factor that affect rate of reaction:

Concentration

concentration increase= rate of rxn increase

Factor that affect rate of reaction:

Pressure (gas only)

pressure increase=rate of rxn increase and more effective collisions

Factor that affect rate of reaction:

Presence of a catalyst

catalyst presence=rate of rxn increase

gives an alternate reaction pathway which requires less energy than the normal

Factor that affect rate of reaction:

Nature of Reactants

Ions in water = fast

gases are FASTER than solids and liquids

ions FASTER than molecules

Catalyst & alternate reaction pathway

lower activation energy

endothermic chemical reaction

exothermic chemical reaction

Heat of Reaction

- change in enthalpy

△H = PE products - PE reactants

-△H=exothermic

+△H=endothermic

Reaction Mechanisms

series of rxn steps that have to occur for a rxn to go to completion that are determined by experimentation

intermediates

species produced in one step that become reactants in a subsequent step

Reaction Rate Laws

rate = k [A][B]

k (specific rate constant)

depends on the size, speed, and kind of molecule at a given temperature

rate law experssion

rate of chemical rxn is proportional to the product of the [ ] of reactants raised to the power of the coefficents

rate of multi-step rxns

product of the [ ] of the reactants in the slowest step

equilibrium

- rates of forward = rate of reverse

- concentrations of reactants and products stay CONSTANT

Solution Equilibrium

when a solution is saturated

Phase equilibrium

rate of condensation/melting = rate of evaporation/freezing

chemical equilibrium

concetration of reactants and products remain constant

rates of forward and reverse are equal

equilibrium expression

Keq

shows the extent to which the reactants are converted to products

AT EQUILIBRIUM

RATES of opposing rxns are EQUAL

solubility product constant

Ksp

values are always SMALL

Le Chatelier's Principle

if stress to a system at equilibrium, the equilibrium will shift to reduce of alleviate the stress

Stressors of system @ equilibrium

- concentration

- temperature

- pressure (only gases)

Describe the shift given that reactants are on the left and products are on the right:

add reactant

right

the other reactants DECREASE as products INCREASE

trying to balance the products by making more so shifts right

Describe the shift given that reactants are on the left and products are on the right:

add product

left

the other reactants INCREASE as products DECREASE

trying to balance the reactants side by making more so shifts left

Describe the shift given that reactants are on the left and products are on the right:

remove reactant

left

the product DECREASES as the reactants INCREASE

trying to balance the reactants side since there isnt enough reactant to make the product

Describe the shift given that reactants are on the left and products are on the right:

remove product

right

the product INCREASES as the reactants DECREASE

trying to balance products side to make more products