chem p2

• mean rate of reaction= quantity of reactant used/ time taken
• mean rate of reaction= quantity of product formed/ time taken
• Factors which affect the rates of chemical reactions include:

  • the concentrations of reactants in solution
  • the pressure of reacting gases
  • the surface area of solid reactants
  • the temperature
  • the presence of catalysts.
• Collision theory explains how various factors affect rates of reactions. According to this theory, chemical reactions can occur only when reacting particles collide with each other and with sufficient energy. The minimum amount of energy that particles must have to react is called the activation energy.
• Increasing the concentration of reactants in solution, the pressure of reacting gases, and the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.
• Increasing the temperature increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction.
• 1. Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts. Enzymes act as catalysts in biological systems.
• Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.
• In some chemical reactions, the products of the reaction can react to produce the original reactants.
• The direction of reversible reactions can be changed by changing

  the conditions.
• ammonium chloride -> ammonium + hydrogen chloride

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• If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case.
• When a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate.
• The relative amounts of all the reactants and products at equilibrium depend on the conditions of the reaction.
• If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change.
• The effects of changing conditions on a system at equilibrium can be predicted using Le Chatelier’s Principle.
• If the concentration of one of the reactants or products is changed, the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again.
• If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.
• If the concentration of a product is decreased, more reactants will react until equilibrium is reached again.
• If the temperature of a system at equilibrium is increased:

  • the relative amount of products at equilibrium increases for an endothermic reaction
  • the relative amount of products at equilibrium decreases for an exothermic reaction.
• If the temperature of a system at equilibrium is decreased:

  • the relative amount of products at equilibrium decreases for an endothermic reaction
  • the relative amount of products at equilibrium increases for an exothermic reaction.
• For gaseous reactions at equilibrium:

  • an increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction
  • a decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction.
• Crude oil is a finite resource found in rocks. Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud.
• Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only.
• Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. The general formula for the homologous series of alkanes

  is CnH2n+2
• The first four members of the alkanes are methane, ethane, propane and butane.
• The many hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation.
• The fractions can be processed to produce fuels and feedstock for the petrochemical industry.
• Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases, are produced from crude oil.
• Many useful materials on which modern life depends are produced by the petrochemical industry, such as solvents, lubricants, polymers, detergents.
• The vast array of natural and synthetic carbon compounds occur due to the ability of carbon atoms to form families of similar compounds.
• Some properties of hydrocarbons depend on the size of their molecules, including boiling point, viscosity and flammability. These properties influence how hydrocarbons are used as fuels.
• boiling point, viscosity and flammability change with increasing molecular size.
• The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised. The complete combustion of a hydrocarbon produces carbon dioxide and water.
• Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules.
• Cracking can be done by various methods including catalytic cracking and steam cracking.
• The products of cracking include alkanes and another type of hydrocarbon called alkenes.
• conditions for catalytic cracking:

  • high temperature
  • catalyst
• conditions for steam cracking:

  • high temperature
  • steam
• The products of cracking include alkanes and another type of hydrocarbon called alkenes.