ROR notes Flashcards
When describing the ROR from a graph what do we always state?
- The speed of the ROR
- How is this ^ shown? + meaning (more product being formed in a given amount of time)
- What causes this? - ie lots of reactant molecules so more frequent successful collisions so more product being formed etc.
^Always mention the frequency of collisions!
State collision theory:
Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy.
^The sufficient energy is known as the activation energy: The minimum amount of energy that particles must have to react.
How do we measure the rate of reaction?
Amount of product formed or Amount of reactant used up/Time (s)
Product formed/Reactant used up can be measured in:
- g (mass)
- cm^3 (volume)
- Moles
So rate of reaction = g/s mol/s or cm^3/s
What is the rate of a chemical reaction determined by?
The frequency of collisions of reactant molecules.
General rate of a chemical reaction:
Fast, then slows down, then stops.
This can be explain with collision theory.
Describe the relationship between the concentration of particles in a solution/gas and the rate of reaction.
Concentration is directly proportional to the rate of reaction.
If we increase the concentration of particles in a solution or in a gas, we increase the rate of reaction.
- As the conc. increases ROR increases.
- Because there are more reactant particles so more successful collisions/higher collision frequency.
- So amount of reactant particles used up/product formed increases.
^This applies to gas and pressure.
RS of surface area and rate of reaction:
- As SA increases rate increases so SA and rate are directly proportional.
- This is bc a larger surface area means reactant particles have a higher chance of colliding with the surface of the solid reactant.
**The smaller the block of reactant, the larger the SA:Volume ratio.
How does temperature affect the rate of reaction?
- Temperature is directly proportional to the rate of reaction.
- As temp increases ROR increases more energy is being supplied to the reactant particles.
- So there is an increase in the movement of particles and therefore more frequent collisions per second.
- As the number of successful collisions per second increases, the transfer of energy between the reactant particles increases.
- Reactant particles now have more energy to overcome the activation energy barrier.
- So even more FQ and more reactant formed.
- So ROR increases.
What are catalysts?
Substances that increases the rate of a chemical reaction but are not used up in them.
How do catalysts affect the reaction profile?
The reaction profile for catalysed reactions will have a lower activation energy (shown by a lower curve).
Why are catalysts useful?
- They can be reused - because they don’t get used up in a chemical reaction.
- They allow use to save money - because they allow use to increase the rate of the chemical reaction without increasing the temperature; this saves energy and money.
How do catalysts increase the rate of a chemical reaction?
- They provide an alternative pathway for the reaction to occur, this pathway has a lower activation energy.
- This means more particles, even those with low energy can cross the activation energy barrier and collide, so there are more frequent successful collisions per second.
- So the ROR increases.
True or false - different chemical reactions require different catalysts?
True or false enzymes are biological catalysts?
True
True
What is meant by a reversible reaction?
A reaction where products can react together to produce the original reactants.
- This is shown by the double arrow.
Factors which affect the rate of a reaction:
- Concentration of reactions in solution.
- The pressure of reacting gases.
- The surface area of solid reactants.
- The temperature of the reaction.
- The presence of catalysts.
Draw a reaction profile for catalysts.
An example of a reversible reaction:
A+B double arrow C+D
Ammonia chloride double arrow ammonia and hydrogen chloride
- In this reaction heating causes the forward reaction and cooling causes the backward reaction.
If a reversible reaction is endothermic in 1 direction, then in the other direction the reaction is?
Exothermic.
^However for each reaction the same amount of energy is transferred.
Endothermic reaction:
Exothermic reaction:
Energy ENTERS - so reaction temp decreases
Energy EXITS - so reaction temp increases.
Hydrated copper sulfate (blue)
RRS:
Forward reaction is:
Backward reaction is:
Anyhydrous copper sulfate (white) + Water
FORWARD = ENDO; heat
BACKWARD = EXO; cool
So if we wna get Anhydrous copper sulfate we heat and to get hydrated copper sulfate we cool.
Anhydrous copper sulfate is:
Hydrated copper sulfate is:
Anhydrous copper sulfate is white
Hydrated copper sulfate is blue
When does equilibrium occur?
Equilibrium occurs when a reversible reaction takes place in a sealed container which prevents any reactant and products from escaping and the forward and reverse reactions occur at the same rate.
What is Le Chatalier’s Principle?
If a system is at equilibrium and a change is made to the conditions, the reaction responds to counteract the change.
If the concentration of a reactant is increased:
- The reaction is no longer at equilibrium.
- Rate of forward reaction increases, equilibrium moves to the left.
- So more product will be formed until equilibrium is reached again.
