Unit 6 Reactions Mechanism

Question 1

Reaction mechanism definition?

Answer 1

Step by step sequence of an elementary reaction

Question 2

Each step in reaction mechanism involves

Answer 2

Small amount of bond breaking and making

Question 3

Elementary reaction

Answer 3

one or more chemical species react directly to form products in a single reaction step

Question 4

Rate limiting step

Answer 4

The slowest step

Question 5

reaction intermediate

Answer 5

the product of one step and the reaction of the other step

Question 5

molecularity

Answer 5

classifying an elementary reaction based on the number of reactant molecules

Question 5

unimolecular reaction

Answer 5

type of elementary reaction involving only one reactant molecule

Question 5

bimolecular reaction

Answer 5

elementary reaction resulting from the collision of two reactant molecules

Question 6

termolecular reaction

Answer 6

elementary reaction involving three reactant molecules

rare

Question 7

why are termolecular reaction rare?

Answer 7

the simultaneous collision of three molecules in the correct orientation is unlikely

Question 8

how do you predict the rate law?

Answer 8

for a question like this, you would be given two elementary reactions and the rate constant

1. find the rate constant of the slower reaction and see if it matches the rate constant given
2. if they do not match, set up an equilibrium expression from the fast reaction which is the concentration of the products over the reactants
3. solve for the concentration of the products
4. plug the reactant side in the for the same molecule in the slow step
5. now see if it matches the known rate law

Question 9

how to write the rate law for an elementary step? units?

Answer 9

rate with units molarity over seconds equals the k the rate constant times the concentration of the reactants

Question 10

what are factors that can affect the reaction rate?

Answer 10

increasing the concentration of reactants

molecules being closer together higher chance of molecules colliding

increase in temperature

Question 11

collision theory

Answer 11

if molecules are not at the right angle a reaction will not occur where one molecule must touch a different atom in another molecule

Question 11

collision theory for bimolecular molecule

Answer 11

for a bimolecular reaction to take place. the two molecules must collide at the correct orientation and larger energy than the activation energy in order for the reaction to occur

Question 11

what is the purpose of a catalyst??

Answer 11

speed up a chemical reaction

Question 11

what does k in the collision theory equation depend on?

Answer 11

the temperature

Question 11

collision theory equation? what does each variable mean?

Answer 11

k=Zpf

Z is the number of collisions

p is the number of correct orientations

f is the number of molecules with sufficient energy

Question 11

does temperature affect the orientation of molecules?

Answer 11

no

Question 11

Does the temperature affect the amount of energy? why?

Answer 11

temperature increases the kinetic energy meaning more molecules will collide at a faster rate and more energy will be produced

Question 12

what is the Arrhenius equation? what does each variable represent? units of each?

Answer 12

k=Ae^(-Ea/RT)

A is the frequency factor and has the same units as k

Ea is the activation energy

R is the gas constant 0.0083145 KJ/mol

and T is the temperature in kelvin

Question 13

what does the Arrhenius equation tell us?

Answer 13

how the rate constant k changes based on activation energy and temperature

as activation energy in inversely proportional to rate constant

temperature is proportional to rate constant

Question 14

what is the formula to solve for Ea? units for Ea?

Answer 14

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

Question 15

what is the Arrhenius equation in the form y=mx+b

Answer 15

ln(k)=(-Ea/R)(1/T) + lnA

y is ln(k)

m is -Ea/R

x is 1/T

b is lnA

Question 16

given a table of data solve for the activation energy?

Answer 16

1. solve for m using y2-y1/x2-x1
2. -Ea/R set equal to the slope solve and isolate for -Ea

Question 17

transition state

Answer 17

the unstable group of atoms representing the highest energy
along the pathway from the reactants to the products

Question 18

activation energy

Answer 18

minimum energy needed to activate a successful reaction

Question 19

how does sufficient energy in k=Zpf behave when temperature increases

Answer 19

the sufficient energy increases exponentially

Question 20

what does the TS theory stand for and what is the Ts theory?

Answer 20

also known as the transition state theory

explains the reaction rates of elementary chemical reactions

Question 21

what is the sufficient energy formula?

Answer 21

f=e^-Ea/RT

Question 22

how does higher T affect Ea/Rt in the arrhenius equation

Answer 22

decreases it

Question 23

how does higher T affect e^x in the arrhenius equation?

Answer 23

decreases it

Question 24

how does higher T affect k in the Arrhenius equation?

Answer 24

increases it

Question 25

how does higher T affect rate in the arrhenius equation

Answer 25

increase it

Question 26

factors affecting the reaction rate

Answer 26

concentration, temperature and catalyst

Question 27

how does concentration affect the reaction rate?

Answer 27

their reaction rate increases when moving molecules are closer together because it increases they likelihood that they will collide

Question 28

how does temperature affect the reaction rate?

Answer 28

Increasing the temperature will increase the rate of the reaction because temperature increases the kinetic energy and molecules with higher energy than the activation energy will collide more often

Question 29

where are catalysts involved?

Answer 29

in the rate-limiting step to speed up the reaction

Question 30

are catalysts consumed in the reaction?

Answer 30

no

Question 31

do catalyzed reaction have the same endo/exothermicity as the uncatalyzed reaction?

Answer 31

yes