Rates of Reaction and Equilibrium
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Define ‘rate of reaction’
The change in concentration of a reactant or product in a given time
What 4 factors change the rate of a chemical reaction?
Concentration Temperature Use of catalyst Surface area of solid reactants
What two conditions have to be met for a successful collision?
Particles collide with correct orientation Particles have sufficient energy to overcome the activation energy barrier of a reaction
Explain the effect of increasing concentration of a reactant
Increased concentration increases number of particles in the same volume Particles are closer together Particles collide more frequently More successful collisions so greater rate of reaction
Explain the effect of increasing pressure of a gas on rate of reaction
Concentration of molecules occupies smaller volume Gas molecules are closer together Collide more frequently More effective collisions Increased rate of reaction
What two ways can the progress of a reaction be followed?
Monitoring removal of a reactant Following formation of a product
What 3 measurable things may change during a reaction?
Gas volume Mass of reactants or products Colour
What two methods can be used to determine rate of reaction if a gas is involved?
Volume of gas produced Monitoring loss of mass of reactants using a balance
What is a catalyst?
A substance that changes the rate of a chemical reaction without undergoing any permanent change itself
How does a catalyst increase rate of reaction?
Provides an alternative pathway of lower activation energy
What is a homogenous catalyst?
A catalyst that has the same physical state as the reactants.
How does a homogenous catalyst work?
Catalyst reacts with reactants to form intermediates Intermediate then breaks down to form product and regenerates the catalyst
Give 2 examples of where homogenous catalysis is used
Making esters with a sulfuric acid catalyst Ozone depletion
What is a heterogenous catalyst?
A catalyst that has a different physical state from the reactants
How does a heterogenous catalyst work?
Reactant molecules are adsorbed onto the surface of catalyst Reaction takes place Product molecules leave surface of catalyst by desorption
Give 3 common processes where heterogenous catalysis is used
Making ammonia Reforming Hydrogenation of alkenes
What are 3 key features of a Boltzmann distribution curve?
No molecules have 0 energy Area under curve is equal to total number of molecules No maximum energy for a molecule
What happens to a Boltzmann distribution curve with an increased in temperature?
Peak shifts right and down
What happens at a higher temperature to the molecules according to Boltzmann distribution?
More molecules have energy greater than or equal to activation energy Greater proportion of collisions leads to a reaction Collisions will be more frequent, but increased energy is more important
Describe the effect of a catalyst on the Boltzmann distribution curve
Shifts Ea to the left so greater proportion of molecules have energy levels greater than or equal to that of the activation energy
What are the two key features of an equilibrium system?
The rate of the forward reaction is equal to that of the reverse reaction Concentrations of reactants and products do not change
How does a reaction remain in equilibrium?
By being a closed system
What does Le Chatelier’s principle state?
When a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change
Explain the importance of catalysts on sustainability
Increased sustainability by lowering temperature demands and reducing energy demands of fossil fuels with resulting reductions in carbon dioxide emissions