CHM1046 Exam 2 Dr.Dillon

Reactions can be spontaneous but

this does not mean they occur fast

Enthalpy

total energy of a system (difference between products and reactants)

Examples of catalysts

Nickel Iron Platinum

Maxwell-Boltzmann distribution

Shows the spread of energies that molecules of gas or liquid have at a particular temperature

intermediates

Those reactants and products that appear only in an elementary reaction but not in the overall reaction

half life formula for zero order

[A]0/2k

homogeneous catalyst

a catalyst that is in the same phase as all the reactants and products in a reaction system -usually dispersed in liquid -less expensive -can be designed to function selectively

catalytic converter

a device that reduces carbon monoxide emissions from vehicles.

reaction rates

a measure of how quickly reactants turn into products

reaction mechanism

a series of elementary reactions that take place during the course of a complex reaction

bimolecular elementary reaction

a+b->products

most important type of homogeneous catalysts in a liquid

acid and base catalyts

the elementary steps must

add up to the overall equation, physically reasonable, correlate with the rate law

catalyts are not

altered

average rates

an overall rate measured over a period or time interval

enzyme catalysis

biological catalysts

X+Y=Z Rate of reaction=?

change in [Z]/change in time

rate of reaction equals

change in concentration/change in time

Reaction occur the fastest when molecules are

colliding quickly

rate of reaction depends on

collision frequency and collision energy

termolecular reaction

elementary step with 3 molecules

cataysts do not affect

enthalpy

spontanueous proccesses

physical or chemical change that occurs with no outside intervention however some energy may be supplied to get the process in action (activation energy)

unimolecular elementary reaction

product

units of k for zero order

mol/L*s

poor orientation=

no reaction

Increasing temperature increases

rate constant

zero order reaction

rate is independent of the concentration of the reactant.

1st order reaction

rate=k[A]

instantaneous rate

rates measured at any point during the reaction

initial rates

rates measured at the beginning of the reaction, which is dependent on the initial concentrations of the reactants

integrated rate law

relationship between the concentrations of the reactants and time

applicatios of kinetics

shelf life, drug metabolism, food preservation, radiation

differential rate law

shows how the rate of reaction depends on the concentration

catalyst

substance that speeds up the rate of a chemical reaction

collisions need

sufficient energy/velocity

integrated rate law tells us

the concentration as a function of time

determining step

the slowest step in a complex reaction

Ina reaction, as the pressure increases

the space in which the particles are moving becomes smaller

Kinetics

the study of reaction rates

chemical kinetics

the study of reaction rates, how reaction rates change under varying conditions and by which mechanism the reaction proceeds.

overall reaction order

the sum of all the exponents in a rate law expression

activation energy

Energy needed to get a reaction started

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.

frequency factor

-"A" in Arrhenius equation -also known as "attempt frequency" -a measure of how often molecules in a certain reaction collide -units of s ^-1

half life formula for second order

1/k[A]0

units of k for first order

1/s

heterogeneous catalyst

A catalyst that is in a different phase from that of the reactant substances.

Enzymes

Catalysts for chemical reactions in living things -highly specific

units of k for second order

L/mol*sec

units for k third order

L^2/mol^2*s

higher order reactions

Reactions in which more than two species are involved, or one species reacts with stoichiometric coefficient >2

2nd-order reactions of Class I

Reactions in which the rate varies with concentration of a single species, but the stoichiometric coefficient is 2. The rate varies with the reciprocal of the concentration, so a plot of 1/(concentration) versus time is linear.

2nd-order reactions of Class II:

Reactions in which the rate varies with the concentration of two species, each of which has a stoichiometric coefficient of 1. A plot of ln(concentration .A/concentration B) versus time is linear.

enzyme-substrate complex

When an enzyme binds to its substrate, it forms:

half life formula for first order

ln(2)/k

rate laws are

how the rate depends on amounts of reactants

Factors that effect the rate of a reaction

increasing temperature, concentration of the reactants, surface area, catalysts, physical states, light, increased pressure

Arhenius equation

k = Ae^(-Ea/RT)

Arrhenius equation

k=Ae^(-Ea/RT); relationship between rates and temperatures

rate law

k[A]^n; works when temp is constant

half life

length of time required for half of the radioactive atoms in a sample to decay

Two-point form of Arrhenius equation

ln (k2/k1) = Ea/R (1/T1 - 1/T2)