2.3 Knetics Flashcards
What is rate in chemical reactions?
Change in concentration of a species over time
What is the concentration unit?
mol/ L OR M
What is the time unit?
seconds
Rate units
M/s
Activation energy
Minimum energy required to initiate a chemical reaction
Difference between reactants and the transition state (on graph)
What is the highest point on a reaction coordinate diagram?
Transition state
What shows the energy change of a reaction, on a graph
Difference between reactants and products
ΔH if enthalpy
Area under maxwell boltzmann distribution = ?
Total number of particles
What happens to maxwell boltzmann distribution hen temperature is INCREASED?
- curve shifts to right
- maximum point / mean value is lower and further to right
- smaller number of particles with low energy
- larger number of particles with energy > Ea (Ea stays same)
- More successful collisions
What does adding catalyst do to maxwell boltzmann distribution?
- Lowers Ea (further to right)
- more particles with energy > Ea
- ∴ rate of reaction increases
How do catalysts speed up reaction?
Form an alternative reaction pathway
What does Km show?
How effectively an enzyme can bind to its substrate
What does Vmax show?
How efficient the enzyme is at catalysing the reaction
What do 0 orders depend on?
Depend on a saturatable enzyme or a saturatable catalyst
Increased surface area …………… rate of reaction
Increases
Why are many powdered substances (eg. Flour) highly flammable?
- carbohydrates with lots of C H and O
- Have a very high SA
- Burn very rapidly if Ea is reached
Increasing pressure …………….., the rate of reaction
Increases
NOTE: Apart from 0 order reactions (eg. When enzyme is saturated)
What is the general rate equation of a reaction?
rate = K [A]* × [B]*
- = power = order wrt agent
Σ powers in a rate equation =
Overall order of reaction
What is K in rate equation?
K = Ae ^(Ea/RT)
A = likelihood of collisions being in correct lineup
R = gas constant
T = Temperature in k
What determines the rate equation?
Slowest step
This has the slowest rate constant (k)
In zero order reactions, rate is equal to….?
Rate = K
What are characteristics of a 0 order concentration time graph
- straight linear line
- gradient = -k
In zero order reactions, the rate is independent to…..
The concentration of reactant
In first order reactions, the rate is….
Proportional to the concentration of a single reactant raised to the first power
What is the shape of a concentration time graph of a first order reaction?
Curve
Doing the log of the graph will give you a straight line graph
In first order reactions, the half lives are….
Constant
They depend in the rate constant K
What is half life?
The time taken for the concentration of a reactant to drop to half its original value
In zero order reactions, the half lives….
Get shorter
In higher order reactions, the half lives…..
Get longer
What is the sum of exponents in a second order reaction?
2
What shape are lines of different orders in graphs with rate against concentration?
0 - straight line parallel to x axis
1st - linear (rate is proportional to concentration) (gradient = k)
2rd - exponential (rate =k²)
What is molecularity?
The number of individual molecules taking part in the rate determining step
Unimolecular rate determining step =
Rate = k[A]
Biomolecular rate determining steps =
Rate = k[A]²
Rate = k[A][B]
Trimolecular rate determining steps =
Rate = k[A]³
Rate = k[A]²[B]
Rate = k[A][B][C]
What can make the same starting materials form different products, in organic and enzyme chemistry?
Different reaction conditions
Must be reversible reaction
2 possible sets of products with different energies
What is the thermodynamic product of a reaction?
One that takes the system to the most stable state
What is used to get to thermodynamic products?
High reaction temperatures
Long reaction times
What is the kinetic product?
The one that’s fastest to get to
Ans has the lowest Ea
What conditions used to form kinetic products?
Low temperature
Short reaction times
Which species appear in rate equation?
Everything upto and including the rate determining step
