8. Reaction rate Flashcards
Rate of reaction definition + formula + units
the change in concentration of a reactant/product per unit of time.
(Δ[P])/Δt or (- Δ[R])/Δt
moles per liter per unit of time (mol/Ls)
The change in concentration can be measured using which properties
mass (solid) or volume (liquid) change
change in pH (only one base/acid present)
change in conductivity
use of a spectrometer or colorimeter (complex ions)
Collision theory
in order for particles to react they must collide with appropriate geometry/orientation and with sufficient energy (equal or greater than activation energy)
The activation energy
the minimum energy that needs to be supplied by molecular collisions for a reaction to occur
Transition state
the configuration of the atoms at the time of the collision (activated complex)
Factors affecting the rate of reaction:
1| Concentration of reactants: rate increases with increasing C(R) – the more particles of the reactant there are, the more collisions occur
2| Pressure: rate increases with increasing p (directly proportional)
3| Temperature: rate increases with increasing T – heat increases molecular movement, increasing the number of collisions
4| Surface area: rate increases with increasing SA
5| Catalysts: increase the reaction rate by decreasing the activation energy
In homogeneous catalysis reactants/products are ___, and in heterogenous catalysis reactants/products are ___.
in the same phase as the catalyst, not in the same phase as the catalyst
The general reaction rate formula
r = - 1/a (Δ[A])/Δt = - 1/b (Δ[B])/Δt = 1/c (Δ[C])/Δt = 1/d (Δ[D])/Δt
The rate law formula + what do the exponents determine
r = 〖k[A]〗^m 〖[B]〗^n
the order of a reaction
How can the rate constant k be changed
by changing the temperature, pressure, surface area, adding a catalyst… - not changed by concentrations of reactants
Half-life definition + formula
the time taken for the concentration of a reactant to fall to a half of its initial value
t_(1/2)= 0.693/k
What does the Arrhenius equation state + state the equation
that the rate constant increases with increasing temperature
lnk= -(Ea/RT)+lnA
