Kinetics - Chapter 5 and 18 Flashcards
What is needed for a reaction to be successful
particles must collide with enough energy and in correct orientation
What is activation energy
the minimum amount of energy needed to start a reaction is called the activation energy
What happens to a reaction when the activation energy is reduced
faster reaction
What is the Maxwell-Boltzmann distribution graph
Graph with energy on the x axis and number of particles on the y axis
Area under the curve is the total number of particles
The peak is the most probable energy
The average energy is just to the right of the peak
What is the rate of a reaction
It is the change in concentration of a substance per unit of time
What factors affect rate
Concentration (pressure)
Surface area
Temperature
Catalyst
What happens to the rate when concentration is increased
Rate increases
More particles in a given volume so more frequent successful collisions will happen
What happens to the rate when surface area is increased
Rate increases
Because particles of a solid are exposed so more chance of a successful collision with other reactant particles
What happens to the rate when temperature is increased
Rate increases
Particles moves faster so collide more often
Many more particles with energy bigger than activation energy
What happens when a catalyst is added
Rate increases
Catalysts provide an alternative reaction pathway with a lower activation energy so more particles have energy above activation energy
How does concentration affect rate
The rate depends on the concentration of the reactants but not all reactants make the same contribution to how fast a reaction goes
What is a rate equation
It is an equation used to show how the rate of a reaction depends on the concentration of the reactants involved
rate = k [A]x [B]y
What is the order of the reaction
The sum of the orders of reaction of each substance
How do you determine the rate equation for a reaction
You need to determine the orders with respect to each of the reactants
What methods are used to find the rate equation
Initial Rate Method
Graphical method
What is the initial rate method
It is when the rates are compared from a series of experiments in which the concentration of only one reactant is varied at a time
What is the graphical method
It is when an experiment is carried out where each reactant varies with time and plot concentration-time graph
The shape indicates the order of each reactant
A second graph is then plotted of rate-concentration by measuring the gradient at different points on the first graph
What is zero order for the graphical method
A straight line with a negative gradient for conc-time graph
A horizontal flat line for conc-rate graph
What is first order for the graphical method
A sloping curve which drops with a constant half-life for conc-time graph
A straight positively sloped line for conc-rate graph
What is second order for the graphical method
The line declines steeply then flattens out for conc-time graph
The line is curved for the conc-rate graph
Straight line for conc2 - rate graph
What happens to the Maxwell-Boltzmann distribution graph when temperature increases
Peak shifts to the right and down
The bit after goes up
What is the rate constant
It is the value of the rate at any particular temperature when the concentration of all species in the rate equation are 1 mol dm-3
What is the Arrhenieus equation
k = Ae -Ea/RT
lnk = -Ea/RT + ln A
What graph do you plot for an Arrhenius plot
1/T on the x axis
ln k on the y axis
Gradient is -Ea/R
y intercept is ln A
What is the rate determining step
It is the slowest step in a reaction mechanism and controls the overall rate of the whole reaction
What is in the rate equation
species that are involved before or during the the rate determining step
What is assumed about the order with respect to a particular reactant
That it shows the number of particles of it participating before or during the rate determining step
What does it mean for a reactant if it is zero order with the rate determining step
The species is present only after the rate determining step
For primary haloalkanes what is the rate equation for the hydrolysis of haloalkanes
rate = k [RX] [OH-]
What is the rate equation for the hydrolysis of tertiary haloalkanes
rate = k [RX]
Why does using a large amount of reactant take them out the rate equation
Because the concentration is almost constant making them zero order
