Past Exam Questions
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Define Rate of Reaction
The change in concentration per unit of any one reactant or product
Explain the term heterogeneous catalysis
Catalysis in which the reactants and the catalyst are in different phases
Describe the surface adsorption theory of catalysis 3 main points
• Reactant molecules diffuse towards and then settle on the surface of a catalyst • The reactant molecules are held on the surface of the catalyst by temporary bonds formed between these molecules and the catalyst • The products leave the surface of the catalyst and the process begins again
Explain what is meant by activation energy
The minimum energy that colliding particles must have for a reaction to occur
State and explain two ways of increasing the rate of reaction, other than by using a catalyst
• Increase concentration of reactants: - Reactants are closer together so there is a greater frequency of collisions between reactants • Increase temperature - Reactants have more energy and therefore move faster which means there is a greater frequency of collisions between reactants
Suggest a reason why NO is not formed in every collision between a pair of NO2 molecules
Colliding NO2 molecules did not reach activation energy
What is a catalyst?
A substance that alters the rate of a chemical reaction but is not consumed in the reaction
Explain how the type of bonding in the reactants influences the rate of a chemical reaction in aqueous solution.
Ionic compounds react quickly in solution as bonds are already broken Covalent compounds react slowly as bonds need to be broken first
How could you reduce the rate of a reaction that takes place in solution?
Lowering the temperature
The diagram shows the oxidation of methanol using platinum wire as catalyst. State one observation made during this experiment.
wire glows and dims Smell of methanol Popping sounds Flame
The diagram shows the oxidation of methanol using platinum wire as catalyst. Identify two major products of the oxidation.
Methanal Water (H2O) Hydrogen (H2)
What term is usually used to describe the attachment of liquid or gaseous molecules to a solid surface?
Adsorption
Explain how this type of interaction between the methanol and the platinum catalyst affects the rate of oxidation.
• Methanol bonds weaken • Higher methanol concentration on surface • Methanol forms temporary bonds on surface • There are more effective collisions between reactants on the surface of the catalyst
Explain how a catalyst poison like sulfur interferes with a catalyst.
The surface of the catalyst is blocked by sulfur
Name two metals used in catalytic converters
Platinum Palladium
What type of catalysis occurs in a catalytic converter?
Heterogeneous
Name a substance that could poison the catalyst of a catalytic converter
Lead
Explain clearly why there is an almost instantaneous reaction between aqueous solutions of sodium chloride and silver nitrate
They are ionic compounds which means their bonds are already broken
Explain effective collision.
A collision that results in the formation of products
Write a balanced equation for the decomposition of hydrogen peroxide
2H2O2 -> 2H2O + O2
Why does the rate of chemical reactions generally decrease with time?
Reactants are gradually used up
Give 3 conditions necessary for a dust explosion to occur
Ignition Oxygen Enclosed space Particles must be dry Particles must be combustible
Name two substances that enter a catalytic converter and name what substances they are converted into
Carbon monoxide enters and is converted to carbon dioxide Hydrocarbons enter and are converted into carbon dioxide and water
What type of catalyst is used during the decomposition of hydrogen peroxide
Heterogeneous