kinetics definitions Flashcards
Chemical kinetics
is the study of the rates of chemical reactions and the factors that affect them
The rate of chemical reaction
the change in the concentration per unit time
What are the factors that affect rate of reaction
the concentration of the reactants involved
temp
physical state of reactants (i.e. powder)
cataylsts
the action of light
What is the first order rate constant?
s-1
What is the zero order rate constant?
mol L-1 s-1
Half life
the time (usually in seconds) for concentration of the reactant to fall to half of its initial value and is denoted by the symbol (t1/2) e.g. for a 1st order reaction t1⁄2 =ln2/k
For a first order reaction does the initial concentration of the reactants change the half life?
No
For a second order reaction does the initial concentration of the reactants change the half life?
Yes- half life depends on initial concentration of reactants
Collision theory
assumes molecules react by breaking and making bonds; in order to do so molecules must collide in correct orientation and with enough energy above Ea E.G. BIMOLECULAR ELEMENTARY REACTION
For an elementary reaction (and ONLY elementary) the order of reaction is
equal to its molecularity
Activation energy
amount of energy required to reach the transition state
transition state/ activated complex
The transition state in an elementary reaction is the point of highest energy between reactants and products
Reactive intermediates
extremely reactive (products that also act as reactants)
Reactive intermediates represent
points of minimum energy
Transition states represent
points of maximum energy
Rate determining step
slowest step
Catalysts
substances that speed up chemical reactions without being consumed in the overall process by lowering the activation energy required for the reaction to take place by taking it along an alternative reaction pathway or holding the reactants in the correct configuration to react
homogenous catalysts
a catalyst that works in the same phase as the reaction itself (e.g. liquid phase acid catalysis)
heterogenous catalysts
a catalyst that works in a different phase as the reaction itself For example: Pt (solid) in the hydrogenation of alkenes (gas).
Explosions
reactions whose rates increase dramatically as the reaction proceeds e.g. hydrogen and oxygen gas explosion
oscillating reactions
generating products in bursts
autocatalytic
reactions that are catalysed by their own products
average rate
is the change in rate over time
instantaneous rate
is the rate at specific point in time during the course of the reaction
rate constant
proportionality constant (k) in rate law e.g. For a 1st order reaction: rate = k[conc^n]
first order reaction
Where the overall reaction order in the rate law is one.
he rate is directly proportional to the concentration of a reactant.
