M3 - Rates of reaction Flashcards
What 2 parts make up collision theory?
1.Particles must collide with sufficient energy
2. They must collide with the correct orientation
Particles must collide in correct orientation
How does a homogeneous catalyst interact with the reactants?
Forms an intermediate
This intermediate breaks down to give the product and regenerates the catalyst
Which factors can change the rate of a chemical reaction?
Concentration
Temperature
Use of a catalyst
Surface area of solid reactants
Define rate of reaction
The change in concentration of a reactant or a product per unit time OR
Rate = Concentration of reactant (or product) / Time
What are the main features of Boltzmann distribution?
No molecules have zero energy
Area under the curve is equal to the number of molecules
No maximum energy
What is a homogeneous catalyst?
Has the same physical state as the reactants.
What is a heterogeneous catalyst?
Catalysis of a reaction in which the catalyst has a different physical state from the reactants (1)
What is the rule of thumb for reaction rate and increasing temperature?
A 10C increase in temperature doubles the rate.
What are the two methods of determining reaction rate, when a gas is produced?
Monitoring the volume of gas produced
Monitoring the loss of mass of reactants
What does a catalyst do?
A substance that changes the rate of a chemical reaction by providing an alternative ath with a lower activation energy without undergoing any permanent change itself.
How does a Boltzmann distribution show the effect of a catalyst?
Activation energy with a catalyst is lower than normal activation energy.
Therefore a greater proportion of molecules exceed the new lower activation energy.
Explain why increasing concentration/pressure has its effect on reaction rate
Concentration increases More particles per unit volume More frequent collisions More successful collisions Rate increases
What is a heterogeneous catalyst?
Has a different physical state from the reactants.
How does a heterogeneous catalyst interact with the reactants?
Usually solids in contact with gaseous reactants or reactants in solution.
Reactants are adsorbed onto the surface, where the reaction takes place.
After the reaction, the products leave the surface by desorption.
A
What effect does increasing concentration/pressure have on reaction rate?
increasing concentration and pressure Reaction rate increases
How does a Boltzmann distribution curve change when temperature is increased?
The peak is lower and shifted to the right
A greater proportion of molecules can overcome the activation energy
C
What effect does increasing temperature have on reaction rate?
Reaction rate increases with greater temprature
What are the benefits of using a catalyst?
Lowers activation energy
Less electricity used
Product made faster and cuts costs and increases profit
Less fossil fuels used cuts emissions of carbon dioxide
Explain why increasing temperature has its effect on reaction rate
with higher temperature Particles have more energy Higher speed Collide more frequently More successful collisions Rate increases
What are the units of rate of reaction?
mol dm-3s-1 or cm3s-1 or gs-1
Give two examples of homogeneous catalysts
Sulphuric acid in the production of esters
Chlorine radicals in ozone depletion
What is a homogeneous catalyst?
Catalysis of a reaction in which the catalyst and the reactants are in the same physical state (1)
What are the main properties of a catalyst?
Not used up in the reaction.
May react with a reactant to form an intermediate or provide a surface for the reaction to take place.
The catalyst is regenerated at the end of the reaction.
Give examples of heterogeneous catalysts
Iron in making ammonia
Platinum or rhodium in reforming
Nickel in hydrogenation of alkenes
Vanadium oxide in making sulphur trioxide
D
How can progress of a chemical reaction be followed?
Monitoring the removal of a reactant.
Following the formation of a product.
