Kinetics Flashcards
Why do most collisions by reactant particles not lead to a reaction?
- Collisions may not have enough energy
- Particles may not be in the correct orientation when they collide
- Collisions may not be between the correct particles
What do high and low activation energies mean in terms of rate of reaction?
High activation energy means its a slow reaction.
Low activation energy means its a faster reaction.
What is the rate of reaction a measure of?
How quickly a reaction happens (i.e its speed)
What is the definition of rate?
The change in concentration of a substance per unit time
What are the 4 things the rate can be affected by?
Concentration (or pressure with gas)
Surface area (solids)
Temperature
Addition of a catalyst
How does an increase in concentration/ pressure affect the rate?
Increasing the concentration/ pressure increases the rate as there are more particles in a given volume so there are more frequent, successful collisions will happen.
How does increasing the surface area affect the rate?
Increasing the surface are increases the rate as more particles if the solid are exposed, so there is more chance of a successful collision with a reactant.
How does increasing the temperature affect the rate?
Increasing the temperature increases the rate as the particles move faster (collide more often) and there are more particles with energy that is bigger than activation energy
How does adding a catalysts affect the rate of reaction?
Adding a catalyst increases the rate as it provides an alternative pathway with a lower activation energy (lowering the activation energy means there are more particles withe energy larger than the activation energy, so there are more successful collisions possible, so the rate increases)
What are the units of k, the rate constant?
m^-2dm^6s^-1
Can catalysts appear in the rate equation?
Yes
What is the only way rate equations can be derived?
Through experiments
What is the arrhenius equation?
ln(k) = -Ea/RT +lnA\
What does Zero order look like on a concentration time graph?
A straight line showing a constant decline in concentration
What does Zero order look like on a rate concentration graph?
Horizontal line (rate does not depend on concentration)
What does First order look like on a concentration - time graph?
A slightly sloping curve which drops with a constant half-life
What does First order look like on a rate - concentration graph?
Sloping line upwards (g=k) as the rate is directly proportional to the concentration
What does second order look like on a concentration time graph?
The curve declines steeply at first then levels out
What does second order look like on a rate concentration graph?
A sloping curve uphill
What does second order look like on a rate- concentration squared graph
A diagonal line sloping upwards. The rate is directly proportional to the concentration squared.
What do rate mechanisms describe?
The sequence of steps in which reactants are converted into products via short lived intermediate species
What is the shortest step in a reaction mechanism and why is it called this?
The Rate Determining step (r.d.s) as its the step which controls the overall rate of the whole reaction
What is the assumption made to do with the order of a particular reaction?
The order with respect to a particular reactant shows the number if particles of it participating before or during the rate determining step
What do we presume about a zero order reactant?
That it is present in the mechanism only after the r.d.s
Halkoalkanes are hydrolysed by hydroxide ions to produce what?
Alcohols
For primary haloalkanes the can equation can be shown to be what (Haloalkane = RX)
rate = k[RX][OH-]
For tertiary haloalkanes the can equation can be shown to be what (Haloalkane = RX)
rate= k[RX]
