Lecture 3 + 4 Flashcards
What is the rate of a reaction?
The CHANGE in CONCENTRATION of a species per unit of TIME.
From a graph how do you measure initial rate of reaction?
Draw a tangent at time of 0.
What 3 ideas does collision theory suggest?
- Reactions occur when particles COLLIDE, however not all collisions result in reactions.
- Particles must possess at least a MINIMUM amount of energy.
- Particles must approach each other in a certain RELATIVE ORIENTATION.
What factors affect rate of reaction?
- The OVERALL number of COLLISIONS occurring.
2. The NUMBER of particles with enough ENERGY to react.
What is the activation energy?
The MINIMUM energy required to INITIATE a chemical reaction.
What is a transition state?
The HIGHEST energy point in the reaction.
In a Maxwell- Boltzmen graph what does the peak show?
Highest number of molecules with a particular energy.
In a Maxwell- Boltzmen graph what does the area under the curve show?
Number of Molecules
When you increase the the temperature of a reaction, why does the rate of reaction increase? (2 Reasons)
- Particle speeds increases so collisions are more FREQUENT.
- Particles have MORE energy to overcome the energy barrier.
When a catalyst is added to a reaction, why does the rate of reaction increase?
Works by providing an ALTERNATIVE reaction PATHWAY with a LOWER activation energy so MORE particles now have the energy to react.
When increasing the surface of a solid reagent/ heterogenous catalyst, why does the rate of reaction increase?
Increases chances of a COLLISION because more particles are exposed.
When increasing the pressure of a gas, why does the rate of reaction increase?
Forces gas particles CLOSER together increasing the FREQUENCY of collisions so rate of reaction increases.
When increasing the concentration of a liquid, why does the rate of reaction usually increase?
LARGER number of particles so MORE collisions.
The rate of reaction depends on what?
Concentration of Reactants.
What is the general form of the rate law?
Rate= k [A]m [B]n
How do you find the order of a reaction?
Add the reaction order of each reagent together.
In a zero- order reaction the rate does not change, what does this mean?
The reaction depends on a catalytic Bottle- neck.
What is a CATALYTIC BOTTLE-NECK?
A CATALYTIC BOTTLE-NECK is where the reaction depends on a catalyse/ enzyme which has limited capacity. At working concentration with all active sites full, there is no effect when adding more substrate.
What is half life of a reaction?
The TIME taken for the CONCENTRATION of a reaction to drop to HALF of its original value
What does half life depend on?
RATE CONSTANT NOT on CONCENTRATION of reactant
Describe each line on a graph for ‘Rate vs Concentration’ for a Zero, First and Second Order reaction. Why are the lines shown like this?
Zero Order- Straight horizontal line. Rate not dependent on concentration of reactants.
First Order- Rate is proportional to concentration of a single reactant.
Second Order- The rate is proportional to the square of the concentration.
Which order of a reaction has a constant half- life?
First Order Reactions.
Describe each line on a graph for ‘Concentration vs Time’ for a Zero, First and Second Order reaction. What happens to half- life of each one?
Zero Order- A straight line showing a constant decline in concentration. Half life decreases as reaction progresses.
First Order- A slightly sloping curve which drops with a constant half life.
Second Order- The curve declines steeply at first then levels out. Half life increases as reaction progresses.
What is the rate determining step?
The overall rate of a multi- step reaction is governed by the SLOWEST step.
