Topics 9+16: Kinetcs I & II Flashcards
Why is rate of reaction controlled?
Safety (too quick can be dangerous)
Cost & efficiency (as cheaply as possible, as quickly as possible)
Collision Theory
reaction = particles colliding with enough energy (Ea) & correct orientation
more successful collision in volume per sec = faster rate
surface area (smaller=faster), concentration & temperature (higher=faster), catalysts (lower Ea so more ps have enough E)
Boltzmann Distribution Curve
nº of ps / Energy
no ps have 0 energy, most have average (middle), few at extremes
molecules past Ea point will be involved in successful reaction
area under curve always maintained, spread changes
e.g higher temp = curve shifted to higher energies
Heterogenous Catalysts
different state from reactants
reactants aDsorb onto surface which weakens their bonds
reactants break, new bonds form & products diffuse away
cause transition states
lower E needed for reaction
Sustainability of Catalysts
Lower temperature: less E needed
reduce demand from fossil fuels & CO2 emissions
(possibly) greater atom econ = less waste
Reaction order
Order of reaction with respect to chemicals, show how rate is affected by changing their concentration
Overall order = sum of individual orders
Rate Equation
rate directly proportional to concentration
R = k[A]ˣ[B]ʸ
K is rate constant, specific to experiment
[] = concentration of reactants in mol/dm3
coefficient in equation tells you index = order
overall order = x + y
C-T GRAPHS: Zero order
Straight line
rate (gradient) doesn’t change with concentration
Half-life decreases over time
C-T GRAPHS: First order
curve, as concentration halves, so does the rate of reaction (gradient)
Half-life is constant
C-T GRAPHS: Second order
-ve exponential
as concentration halves, rate (gradient) goes down exponentially
half-life increases over time
Half-Life
time taken for concentration of a reactant to reduce by half
Rate-Determining Step
slowest step in reaction mechanism
what is measured when rate is measured as other steps occur too quickly
R = k[A] means A is rate-det step
Arrhenius Equation
ln(k) = ln(A) - (Ea/R)(1/T)
A = Arrhenius constant, R = gas constant
T = temperature in Kelvin
in K/T graph, m = -Ea/R so activation energy can be determined
Rate/Concentration Graphs
Zero order: horizontal line
First order: straight increasing line
Second order: quadratic increasing (rate = concentration^2)
Initial rates
Used to determine order
Doubling concentrations means: zero = unchanged, first = initial rate x2, second = initial rate x4 (x2^2)
