Chemistry Paper 2

• Rate of a Chemical Reaction

  Gradient of Line
• Finding the rate of a chemical reaction

  1. Monitoring the amount of reactants used over time

  2. Monitoring the amount of products made over time
• Gradient of a line on the graph

  • Tells you the rate of the reaction at that time
  • Steeper the gradient, the faster the reaction
• Calculating rate of reaction at a time

  Draw tangent to curve & calculate gradient
• Increasing the temperature


  Reactions happen more quickly
• Increasing the temperature

  Increases the rate of reaction because particles collide more frequently
• Increasing the concentration of reactants

  Increases the frequency of collisions between particles, and so increases the rate of a reaction
• Increasing the pressure of reacting gases

  Increases the frequency of collisions, and so increases the rate of a reaction
• Collision Theory


  • Particles must collide, with a certain minimum amount of energy, before they can react
  • The minimum amount of energy that particles must have in order to react is called the activation energy of a reaction
• Surface area

  The rate of a chemical reaction increases if the surface area to volume ratio (SA: Volume) of reactants is increased
• Catalyst

  Speeds up the rate of a chemical reaction but is not used up itself during the reaction
• Different catalysts are needed for different reactions
• Positive factors of catalysts

  Used whenever possible in industry to increase rates of reaction & reduce energy costs
• Dynamic Equilibrium

  In a reversible reaction, the rate of the forward and reverse reactions is at equal equilibrium in a closed system
• Reversible reaction

  The products of the reaction can react to make the original reactants
• Endothermic reaction


  Requires energy input (forward reaction)
• Exothermic reaction

  Releases energy (backward/reverse reaction)
• Hydrocarbon

  Molecule containing only hydrogen and carbon atoms
• Crude oil is a mixture of many different hydrocarbon compounds
• Alkanes


  Saturated hydrocarbons containing as many hydrogen atoms as possible
• Fractional distillation

  Crude oil separated into fractions based on boiling points
• Fractions


  Separated hydrocarbons based on boiling points
• Lighter fractions


  Make better fuels as they ignite more easily and burn cleaner
• Combustion of hydrocarbons

  Carbon and hydrogen are oxidised to produce carbon dioxide and water
• Incomplete combustion of hydrocarbons produces carbon monoxide
• Cracking hydrocarbons

  Breaking down large hydrocarbon molecules into smaller alkanes and alkenes
• Pure substance

  Has a fixed melting and boiling point
• Impure substance

  Mixture of different elements or compounds
• Using chromatography


  To analyse unknown substances in a solution and identify them by comparing Rf values
• Life Cycle Assessments (LCAs)

  Assess the environmental impacts of products, processes or services at all stages of the life cycle
• Exploiting Earth's limited materials has social, economic and environmental issues
• Recycling metals saves energy and finite metal ores
• Sewage treatment

  1. Screening to remove large solids & grit

  2. Sedimentation to produce sewage sludge

  3. Aerobic biological treatment of the separated effluent
• Sewage sludge

  Separated, broken down by anaerobic digestion and dried, can be used as fertiliser
• Purifying water for drinking

  Passing it through filter beds, adding chlorine, ozone or UV light to remove solids and microorganisms
• Desalination


  The removal of salt from water using membranes
• Earth's early atmosphere

  Consisted of CO2, nitrogen, H2O vapour, traces of methane and ammonia
• How oxygen increased in the atmosphere

  Photosynthesis by algae reduced CO2, formation of fossil fuels and sedimentary rocks containing carbon reduced CO2
• Nitrogen oxides from high temperature engines cause breathing problems and acid rain
• Today's atmosphere is 80% nitrogen, 20% oxygen, with small proportions of CO2, water vapour and noble gases