Test 2 Flashcards
chemical kinetics
the study of the rate of the chemical reaction and the factors that affect it
reaction rates can be measured by
the disappearing reactants or by the appearing products
average reaction rate
change in the measurable quantity of a chemical species/change in time
average reaction rate must be
positive
if finding the instantaneous rate
find the slope of the tangent line
determining measurable quantity: solids
-change in volume with a graduated cylinder, caliper, ruler
-change in mass with a balance
determining measurable quantity: liquid
-change in volume with a graduated cylinder, pipette
-change in mass with a balance
determining measurable quantity: solution
-take aliquots of solutions and perform titrations to calculate change in concentration
-take aliquots and use a spectrophotometer to measure color change(change in concentration)
-take aliquots and measure pH to see change in concentration
determining measurable quantity:gas
-change in volume with a eudiometer
-change in pressure with a manometer
factors that affect the rate: surface area
increase the surface area of solids, more molecules are exposed and can react
factors that affect the rate: concentration
-increasing the concentration of a solution allows more molecules to react
-increasing the concentration of gases increases the number of molecules reacting and increases the partial pressure of the gas
factors that affect the rate: temperature
-most significant factor that affects reaction rate
-increasing temperature increases the movement of reactants and applies force when they collide
-temperature is directly proportional to kinetic energy
-for most chemical reactions, raising the temperature 10 degrees C, will double the rate of reaction
factors that affect the rate: nature of reactants
differences in molecular size, electronegativity, pH, polarity, and other factors affect the rate of a reaction
factors that affect the rate: catalysts
-substance that speeds up a chemical reaction but does not get used up in a reaction
inhibitor
substance that slows down a chemical reaction by interacting with a reactant
state of matter rxn rate
solid<liquid<gas<solution
collision theory
states that the rate of a reaction depends on the number of collisions between reactants and fraction of collisions that produce a product
number of collisions between reactants
affected by temperature, concentration, and surface area
fraction of collisions that produce a product
affected by catalysts and temperature
factors that make effective collisions between reactants
- geometric shape of the reactants
- collision geometry(angle of collision)
- activation energy
activation energy
amount of energy required to make a reactant react
enough E must be provided to overcome
repulsion forces of electron clouds and break the bonds of reactants
pH=
-log[H+]
rate law
expression of reaction rate in terms of concentration of the reactants
reaction rate=
K[A]^x[B]^y
reaction order
the power that the concentration of each reactant is raised to that indicates that reactant’s effect on reaction rate
reaction order requirements
-must be determined experimentally
-initial rates data must be used
initial reaction rate
rate at the beginning of a chemical reaction when concentrations of reactants are highest
zero order
when the concentration of the reactant is doubled, there is no effect on reaction rate
1st order
when the concentration of the reactant is doubled, the reaction rate doubles
2nd order
when the concentration of the reactant is doubled, the reaction rate quadruples
overall reaction order
sum of the reaction orders of all the reactants in a reaction
rate constant(k)
proportionality constant that relates the reaction rate to the concentration of the reactants
k requirements
-must be determined using experimental data
-specific for a chemical reaction
-the units for k depend on the reaction order of the reactants
-changing concentrations of reactants has no change on the value of k
-determined at a specific temperature
-adding a catalyst increases k
reaction mechanism
series of steps or smaller reactions that make up an overall reaction
elementary process
step in a reaction mechanism
catalyst
chemical species that is present at the beginning of a reaction, used up in a later reaction, and reformed by the end of a reaction
intermediate
chemical species that forms in an elementary step and is used up before the reaction is completed
molecularity
number of reactant species in an elementary step
having 1 reactant
unimolecular
having 2 reactants
bimolecular
having 3 reactants
termolecular
rate determining step(rds)
slowest elementary step that can be used to write a temporary rate law
temporary rate law
rate law written without using initial rates data and must be verified experimentally; uses k’
integrated rate law
expression of a reactant concentration as a direct function of time
-relate directly to overall reaction orders
zero order integrated rate law
[A]= -Kt + [Ao]
first order integrated rate law
ln[A]= -Kt + ln[Ao]
second order integrated rate law
1/[A]= Kt + 1/[Ao]
nth order integrated rate law
1/[A^n-1]= Kt + 1/[Ao^n-1]
half-life(t1/2)
time it takes for 1/2 of a reactant concentration to be used up in a reaction
-directly related to the overall reaction
zero order half-life
[Ao]/2K
first order half-life
ln(2)/K
second order half-life
1/K[Ao]
each successive reaction order is
twice the amount of time as the previous order
