Theories of Chemical Kinetics Flashcards
What does Collision Theory say?
Particles must collide in order to react.
What is an effective collision?
A collision in which particles have sufficient energy and correct orientation to react
Does an effective collision always lead to a reaction?
Not always
If there are 3 particles of reactant A and 2 particles of reactant B, how many possible collisions are there?
6 (2 x 3)
What is the orientation probability factor (p) ?
The ratio of effectively-oriented collisions to all possible collisions
Does a more complex reactant structure mean a smaller or larger value for orientation probability factor (p) ?
Smaller
What is activation energy (Ea)?
The energy needed to convert reactants to an activated, or transition, state. It is an energy threshold colliding molecules must exceed in order to react.
What are the units for activation energy (Ea)?
kJ/mol or J/mol
Does a higher activation energy (Ea) mean a faster or slower reaction?
Slower because it takes more energy for the reaction to occur
Transition State Theory says that an effective collision of particles leads to the formation of what?
A transition state
What is a transition state?
An unstable species with partial bonds partway between the reactants and products.
The energy to form a transition state is also known as what?
Activation energy (Ea)
A transition state exists at the point of maximum
__________________
(fill in the blank)
Potential energy
As temperature increases, what happens to the rate constant k?
k increases exponentially
Does temperature have a minor or major effect on collision frequency?
Minor effect
Does temperature have a minor or major effect on collision energy?
Major effect
What is Ea (fwd), the activation energy for a forward reaction?
The energy difference between reactants and the transition state
What is Ea (rev), the activation energy for a reverse reaction?
The energy difference between the transition state and the products
What formula do you use to find ΔHrxn from Ea(fwd) and Ea(rev)?
ΔHrxn = Ea(fwd) - Ea(rev)
In an endothermic reaction, do products or reactants have more energy?
Products
In an exothermic reaction, do products or reactants have more energy?
Reactants
In an endothermic reaction, which is bigger, Ea(fwd) or Ea(rev)?
Ea(fwd)
In an exothermic reaction, which is bigger, Ea(fwd) or Ea(rev)?
Ea(rev)
What is the Arrhenius equation?
k = Ae^-Ea/RT
k = rate constant
Ea = activation energy
A = frequency factor
T = temp in K
R = gas constant 8.314 J/mol(K)
If you know k at 2 temperatures, what formula do you use to find Ea?
Ea = R(ln (k2/k1))(1/T1 - 1/T2)^-1
R = gas constant 8.314 J/mol(K)
How do you find activation energy from the potential energies of the transition state and of the reactants?
Ea = Energy of transition state - energy of reactants
