Chapter 13

Question 1

Factors that influence rxn rate

Answer 1

1. Physical states of the reactants
   
   1. the more frequent particles interact(collide), the faster they can react with each other
      
      1. rxns in solid phase are a lot slower than liquids and gases
2. Concentration of reactants
   
   1. greater quantities(as seen through higher conc) = rapid rxn rates
3. Temperature
   
   1. As temp inc, the probability of collisions inc, so rxn rate inc
4. Catalysts
   
   1. accelerate rxns without being consumed themselves

Question 2

initial rate

Answer 2

the rate of a reaction at t=0, immediately after the reactants are mixed

use slope of tangent line to calculate

Question 3

reaction order

Answer 3

• an experimentally determined number defining the dependence of the reaction rate on the concentration of a reactant

Question 4

rate law

Answer 4

• an equation that defines the experimentally determined relation between the concentrations of reactants in a chemical rxn and the rate of the rxn
  
  • relationship btwn reactant concentration and rxn rate

Question 5

rate constant

Answer 5

the proportionality constant that relates the rate of a rxn to the concentrations of reactants

Question 6

overall rxn order

Answer 6

• the sum of the exponents of the concentration terms in the rate law
• reaction rate depends on the concentration of the reactants, but the rate constant does not

Question 7

integrated rate law

Answer 7

• a mathematical expression that describes the change in concentration of a reactant in a chemical rxn with time

Question 8

half-life(t_1/2)

Answer 8

• the time in the course of a chemical rxn during which the concentration of a reactant decreases by half
  
  • high rxn rate=shorter half-life
    
    • inversely related
  • since conc is not a factor in half life formula (t_1/2=0.693/k), half-life of a first order rxn is constant throughout the rxn and independent of conc

Question 9

activation energy(Ea)

Answer 9

• the minimum energy molecules need to react when they collide
  
  • usually kJ/mol
  • always positive
    
    • greater Ea = slower rxn rate
  • According to KMT, higher temp=higher avg kinetic energy
    
    • inc in temp of molecules means that more of them have the minimum amount of energy needed to overcome the Ea of a rxn and react with each other

Question 10

Arrhenius equation

Answer 10

an equation relating the rate constant of a rxn t absolute temperature(T), the activation energy(Ea), and the frequency factor(A)

basically how temp affects rxn rate

Question 11

frequency factor(A)

Answer 11

• the product collision frequency and a term that accounts for the fact that not every collision results in a chemical rxn.

Question 13

activated complex

Answer 13

• a species formed in a chemical rxn when molecules have both the proper orientation and enough energy to react with each other
  
  • have extremely short life spans and fall apart rapidly either forming products or re-forming reactants

Question 14

transition state

Answer 14

a high-energy state between reactants and products in a chemical rxn

the top of the humps

Question 15

reaction mechanism

Answer 15

• a set of steps that describe how a rxn occurs at the molecular level; the mechanism must be consistent with the experimentally determined rate law for the rxn

Question 16

intermediate

Answer 16

• a species produced in one step of a rxn and consumer in a subsequent step
• not considered reactants or products
  
  • Ex. activated complexes?

Question 17

molecularity

Answer 17

the number of ions, atoms, or molecules involved in an elementary step in a rxn.

Question 18

rate determining step

Answer 18

the slowest step in a multistep chemical rxn.

Question 19

catalysts

Answer 19

• a substance added to a rxn that icnreases the rate of the rxn but is not consumed in the process
  
  • homogenous catalyst: when a catalyst and the reacting species are in the same phase
  • heterogenous catalyst: when a catalyst is in a different phase from the reactants
• lowers activation energy –> increases both forward and backward rate of rxn
  
  • system reaches equilibrium more quickly, but doesn’t change k

Question 20

catalytic converters

Answer 20

• Metals are used in catalytic converters in car exhausts
• Two roles:
  
  • to speed up oxidation of carbon monoxide to CO2 and of unburned hydrocarbons to CO2 and water vapor
  • to convert NO and NO2 into N2 and O2

Question 21

enzymes

Answer 21

• large biomolecules(proteins) called enzymes are highly selective catalysts
• Enzymes are specific and substrate fits into active site of an enzyme
  
  • then substrate is converted into product via a pathway that has a lower-energy transition state

Question 22

biocatalysis

Answer 22

• the use of enzymes to catalyze rxns on a large scale; it is becoming especially important in processes that involve chiral(property of inorganic) materials
  
  • deals with both isolated enzymes and microorganisms, it is considered a special type of heterogeneous catalyis.