Studied by 3 people
Rate of reaction
Change in concentration of a particular reactant/product per time
Instantaneous reaction rate
Vinst = |dc|/dt
Initial reaction rate
Instantaneous rate measured at t = 0 (draw tangent line)
Collision theory
Allows the particles to collide non-elastically and undergo chemical changes
Collision theory and KE
KE of most particles is insufficient for breaking chemical bonds
A collision between two fast-moving particles might be violent enough to break or rearrange chemical bonds and transform the reactants into products
Orientation of colliding particles is also important
Reaction of species
Species react as a result of collisions of sufficient energy and proper orientation
For a chemical reaction to occur:
Two or more particles must collide with each other
Colliding particles must have the correct mutual orientation
The sum of KE of particles must be sufficient to initiate the reaction
Factors affecting reaction rate
Concentration, Temperature, Surface area, pressure(gas), catalyst
Activation energy
The minimum energy that colliding particles need for a successful collision leading to a reaction.
Difference in energy between the reactants and transition state
KE > Ea → successful collision
Transition state
Least stable arrangement of atoms in reacting species
Maxwell-Boltzman energy distribution curve
The plots of statistical distribution of the energies at various temperature
Catalyst
Increase the rate of reaction by providing an alternative reaction pathway with lower Ea (reduces Ea).
Reacts with a reactant to form an unstable compound(intermediate)
Intermediate goes through further chemical changes.
Catalysed reactions
Proceed in different steps → each step requires less energy than uncatalysed reaction
Reaction mechanism
Many reactions occur in a series of chemical changes across multiple intermediates and transition states.
A sequence of these changes are called reaction pathway
Multistep reaction
Involves one or more elementary step
Molecularity
Determined by the number of species involved in an elementary step
Unimolecular = involves a single species
Bimolecular = involves two colliding species
Termolecular = involves three species colliding at same time
Rate-determining step
Slowest step
Limits the overall rate of reaction for any given concentrations of reactants
Has the highest Ea
Rate equation
Depends on the mechanism of the reaction
Expression describing the proportionality of the rate to the reactant concentrations
Rate constant k is temperature dependent
Reaction order
zero = rate is independent of the reactant concentration
first = rate is proportional to reactant concentration
second = rate is proportional to [A]2
Arrhenius equation
Uses the temperature dependence of the rate constant to determine the activation energy
Arrhenius factor takes into account the frequency of collisions with proper orientation.
Note
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