chem paper 2

• Rate of reaction


  How quickly a reaction happens
• Mean rate


  The rate could be changing over the time you measure, so this technically gives you the mean rate
• Experiment to measure rate of reaction

  1. Reacting hydrochloric acid and sodium thiosulfate in a conical flask

  2. Measuring the time until the solution becomes cloudy (increased turbidity)

  3. Repeating at different temperatures
• Increasing temperature


  Decreases the time taken for the reaction
• Experiment to measure rate of reaction

  1. Measuring the volume of gas produced using a gas syringe

  2. Plotting a graph with quantity on y-axis and time on x-axis

  3. Drawing a tangent to find the rate at any time
• Ways to increase the rate of a reaction

  • Increasing the concentration of reactants in solution
  • Increasing the pressure of gas reactants
  • Increasing the surface area of solid reactants
  • Increasing temperature
  • Adding a catalyst
• Reversible reaction


  Reactions where the products can return to the original reactants
• Equilibrium


  The point where the rates of the forward and reverse reactions are equal, so there is no overall change
• Increasing pressure


  Favours the forward reaction in a reversible reaction
• Increasing temperature


  Favours the endothermic (reverse) reaction in a reversible reaction
• In a reversible reaction, if the forward reaction is exothermic, the reverse reaction must be endothermic, and vice versa
• Crude oil


  A mixture of hydrocarbons formed from buried plankton
• Alkane names


  • Methane
  • Ethane
  • Propane
  • Butane
  • Pentane
  • Hexane
• Fractional distillation of crude oil

  1. Heating to evaporate and separate into fractions based on boiling point

  2. Longer alkanes have higher boiling points and condense lower in the column
• Crude oil fractions


  • LPG (gases up to 4 carbons)
  • Petrol
  • Kerosene
  • Diesel
  • Heavy fuel oil
• Viscosity


  The thickness or resistance to flow of a liquid
• Longer alkane fractions have higher viscosity
• Alkenes


  Hydrocarbons with a carbon-carbon double bond
• Unsaturated


  Having a carbon-carbon double or triple bond
• Testing for alkenes


  Adding bromine water, which turns colourless if an alkene is present
• Cracking


  Breaking down longer alkanes into shorter alkanes and alkenes
• Catalytic cracking


  1. Using a zeolite catalyst at around 550°C

  2. Steam cracking uses even higher temperatures over 800°C without a catalyst
• Melting point and boiling point


  Tests to determine if a substance is pure
• Formulation


  A mixture designed for a specific purpose, with carefully controlled quantities of components
• Chromatography


  A technique to separate the components of a mixture
• Melting point/Boiling point


  Way to tell if a substance is pure - should be a very specific temperature
• Formulation


  Mixture that has been specially designed to be useful in a very specific way with very specific quantities of different substances
• Chromatography


  1. Separating substances in a mixture

  2. Stationary phase (e.g. chromatography paper)

  3. Mobile phase (e.g. water) rises up paper due to capillary action

  4. Draw line at bottom in pencil

  5. Measure how far solvent and substances have moved to calculate Rf value
• Rf value is a ratio of how far a spot has moved compared to the solvent, between 0 and 1
• Rf values can be compared to known values to identify substances in a mixture
• Testing for elements


  1. Hydrogen - squeaky pop with burning splint

  2. Oxygen - relights glowing splint

  3. Carbon dioxide - turns lime water cloudy

  4. Chlorine - bleaches damp blue litmus paper
• Carbonates react with acids to produce carbon dioxide gas
• Atmospheric composition


  Originally mainly nitrogen and carbon dioxide, then carbon dioxide dissolved in oceans, then reduced by photosynthesis
• Greenhouse gases (water vapour, carbon dioxide, methane) absorb infrared radiation and keep the Earth warm
• Carbon dioxide levels have increased since the Industrial Revolution, contributing to global warming
• Carbon monoxide is an atmospheric pollutant that binds to red blood cells, reducing oxygen transport
• Fossil fuel combustion releases sulfur dioxide and nitrogen oxides, causing acid rain and breathing problems
• Particulate matter (soot) from incomplete combustion can also cause health issues
• Sustainability


  Meeting current resource needs without compromising future generations' ability to do the same
• Potable water


  Water with low enough salt and microbe levels to be safe for drinking