Kinetics Flashcards
What is kinetics: based on? Used suspects? Questions answered?
Time
k, rate
How feel/slow & what will [ ] be at t(time)
General rates
Change in something/time
Change in position(distance)/time
Ex. mph, cm/s
Chemical rates
Rate=🔺[species]/🔺t
Coeff=moles of a species in a rxn
(-) or (+) means conc. increasing or decreasing (respectively)
Collision model
- species must collide in order to react
- not all collisions result in a reaction
check notes for visual
Factors that govern chemical rate
- Concentration: as [react.]^, rate ^
- Temperature: as T^, rate ^
- Activation energy: as Ea^, rate v
- Steric orientation: A^, rate v
Arrhenius Equation
k=Ae^(-Ea/RT)
- R=8.314 J/kmol
[react]^= k(—), rate^
T^= k^, rate^
A^= k^, rate^
Ea^= kv, ratev
Differential rate law
aA+bB -> cC+dD
Rate=k[A]^m*[B]^n
What does the rate law tell us about the rds (what the order means)
The rate at which the reaction takes place, zero or first or second order, but overall rxn is third order
Determining the rate law from an elementary mechanistic step
Coeff tell the order
The missing m and n
Integrated rate law
- Zero, first and second order
- makes [react] to t
Relationship between the slope between the best fit line and the rate constant
- According to rxn, linear line and (-)/(+) direction determines the rate order
Half-life
- Times it takes for 1/2 of reactants to be consumed
1. t1/2=50%
2. t1/2=25%
3. t1/2=12.5%
Half life of first order reaction
ln[A]t=-kt+ln[A]o
ln[A]t-ln[A]o=-kt
ln([A]t1/2/ln[A)o)=-kt1/2
ln(1/2[A]o/[A]o)=-kt1/2
ln(1/2)/-k=t1/2
- only for first order
Rxn coordinate diagrams
- exothermic rxn: react>prod neg change H
- endothermic rxn: react<prod pos change H
Intermediate species
- species made in the middle of rxns
- ex. AC is the intermediate species in the following:
A+BC->AC+B
AC+D->A+CD
Activated complex
- an unstable species created at the peak of a rxn
check notes for example
Activation energy (including the effect of a catalyst)
- amt of energy required for a rxn to take place
- catalysts lower this energy
Catalysts effect on Activation energy
- lowers the energy amount used
check notes for diagram
Homogeneous catalyst
- same phase as reactants
- can be consumed in step 1 and regenerated in a subsequent step
Heterogeneous catalyst
- different phase than reactants
- reactants are adsorbed onto surface of catalyst
- products are released
