C1

• Particle theory


  • Explains how particles in a material behave in each state of matter
  • Considers each particle as small, solid, inelastic sphere
• Solids


  • Strong forces of attraction between particles, hold them close together in fixed positions
  • Particles don't move from their positions, so solids keep definite shape and volume
  • Particles vibrate about their positions, more vibration with higher temperature causes slight expansion
• Liquids


  • Weaker forces of attraction between particles, randomly arranged and free to move past each other but tend to stick closely together
  • Definite volume but no definite shape, will flow to bottom of container
  • Particles in constant random motion, faster motion with higher temperature causes slight expansion
• Gases


  • No attraction between well-separated particles, free to move in straight lines
  • Don't keep definite shape or volume, will fill any container
  • Particles in constant random motion, faster motion with higher temperature causes expansion or pressure increase
• Particle theory is a great model for explaining the three states of matter, but it isn't perfect as the particles aren't solid or inelastic spheres, and the model doesn't show the forces between them
• Changing state


  1. Heating solid increases particle vibration, weakening forces until melting point where particles break free and solid becomes liquid

  2. Heating liquid increases particle motion, breaking bonds until boiling point where liquid becomes gas

  3. Cooling gas allows bonds to form between particles, becoming liquid (condensation)

  4. Cooling liquid allows more bonds to form, becoming solid (freezing)
• The amount of energy needed for a substance to change state depends on the strength of the forces between particles
• The changes of state that occur in the water cycle can be described using the particle model
• Predicting state of a substance

  • If temperature is below melting point, it's a solid
  • If temperature is above boiling point, it's a gas
  • If temperature is between melting and boiling points, it's a liquid
• The bulk properties of a material, like melting point, depend on how the particles interact together, not just the properties of a single particle
• Atomic symbols


  One or two letter symbols representing atoms of each element, a type of shorthand
• Molecular formula


  Shows the number and type of atoms in a molecule
• Displayed formula


  Shows the structure and covalent bonds in a molecule as a picture
• Prefixes for number of atoms

  • Mono (one)
  • Di (two)
  • Tri (three)
• Common molecular formulas

  • Water (H2O)
  • Hydrogen (H2)
  • Ammonia (NH3)
  • Chlorine (Cl2)
  • Carbon dioxide (CO2)
• Ionic compounds


  Form giant lattices instead of individual molecules, so their formulas show the ratio of elements rather than exact numbers
• The names of ionic compounds don't include prefixes to indicate the numbers of atoms, you have to figure that out from the charges on the ions
• Balancing chemical equations


  Adjusting the numbers in front of formulas to ensure the same number of atoms of each element on both sides
• Exothermic reaction


  Gives out energy to the surroundings, usually shown by an increase in temperature
• Endothermic reaction


  Takes in energy from the surroundings, usually shown by a decrease in temperature
• Reaction profile


  • Shows the energy levels of reactants and products
  • Exothermic reactions have products at lower energy than reactants
  • Endothermic reactions have products at higher energy than reactants
• Activation energy


  Minimum energy needed to start a reaction, shown as the difference between reactants and highest point on reaction profile
• Activation energy


  The minimum amount of energy needed for bonds to break and a reaction to start
• Activation energy


  1. Energy needed to start a reaction

  2. Difference between reactants and highest point on reaction profile curve

  4. If energy input is less than activation energy, there won't be enough energy to start the reaction - so nothing will happen
• Greater activation energy


  Bigger difference between energy of reactants and top of reaction profile curve
• Greater energy change


  Bigger difference between energy of reactants and energy of products
• Measuring temperature changes


  1. Put polystyrene cup with known volume of one reagent

  2. Add measured mass/volume of second reagent and observe temperature change

  3. If temperature increases, reaction is exothermic. If temperature decreases, reaction is endothermic
• Dissolving salts in water

  • Dissolving ammonium chloride decreases temperature - endothermic
  • Dissolving calcium chloride increases temperature - exothermic
• Neutralisation reactions


  • Most are exothermic, e.g. HCl + NaOH → NaCl + H2O
  • Reaction between ethanoic acid and sodium carbonate is endothermic
• Displacement reactions


  Generally exothermic, e.g. zinc powder and copper sulfate forming zinc sulfate and copper
• Bond energies


  • Energy must be supplied to break bonds (endothermic)
  • Energy is released when new bonds are formed (exothermic)
• Bond energy calculations


  1. Use known bond energies to calculate overall energy change for a reaction

  2. Positive energy change means endothermic, negative energy change means exothermic
• Evolution of the atmosphere

  1. Phase 1: Volcanoes released gases to form early atmosphere of CO2, N2, H2O, SO2, CH4

  2. Phase 2: Oceans, algae and plants absorbed CO2, produced O2

  3. Phase 3: Green plants and algae produced O2 via photosynthesis, leading to current atmospheric composition
• Evidence supports this explanation of atmospheric evolution, e.g. ancient rock formations, fossil record
• Combustion reactions


  • Example of oxidation reactions
  • Complete combustion of hydrocarbons produces CO2 and H2O
  • Incomplete combustion produces CO, soot, other carbon-based products
• Carbon monoxide


  Toxic gas that can combine with haemoglobin and reduce oxygen supply
• Sulfur dioxide and nitrogen oxides

  • Released from burning fossil fuels containing sulfur and nitrogen
  • Form acid rain when mixed with clouds
  • Contribute to smog and respiratory problems
• Reducing emissions


  1. Removing sulfur from fuels before burning

  2. Using acid gas scrubbers on power stations

  3. Fitting catalytic converters on vehicles

  4. Reducing fossil fuel usage
• Greenhouse gases


  Absorb and re-emit infrared radiation, causing greenhouse effect and warming the Earth
• Increased CO2 levels


  Correlated with increased global temperatures and climate change