Limestone & rate of chemical change

• activation energy is the minimum energy particles must collide with to react
• Rate of reaction is affected by:

  1. temperature
  2. pressure
  3. surface area
  4. concentration
  5. catalysts
• Rate of collisions - temperature

  at higher temperatures, particles have more energy and move faster so particles collide harder and more often meaning more chance of collision having activation energy per unit of time
• Rate of collisions - pressure

  At higher pressures, there's the same number of particles in a smaller area so the number of collisions increase meaning more chance of collisions having activation energy per unit of time
• Rate of collisions - Concentration

  At higher concentrations, more particles are in the same area so more collisions between particles meaning more chance of collisions having activation energy per unit of time
• Rate of collisions - Surface area

  At higher surface areas, more particles are exposed so more collisions between particles meaning more chance of collisions having activation energy per unit of time
• Rate of collisions - catalysts 


  they speed up reactions as they lower the energy required for a collision to be successful
• steepest part of graphs means the fastest reactions as theres highest concentration of all reactants and more collisions having activation energy
• curved line on graphs means the rate of reactions slows down as reactants been used up and theres less successful collisions
• horizontal line on graphs mean reaction finished because all or one reactant is used up or theres no successful collisions
• rate of reaction = change in concentration / change in time
• if volume produced in reaction doesnt change that means that the same amount of all reactants used or not all reactant amount increased
• thermal decomposition is breaking down using heat
• more reactive elements form more stable compounds
• use a gas syringe to record an accurate number of gas
• endothermic absorbs heat
• exothermic releases heat
• if you heat a piece of calcium carbonate (limestone) then allow it to cool you will have calcium oxide (quicklime)
• if you add water to calcium oxide (quicklime) then you have made calcium hydroxide (slaked lime)
• add more water to calcium hydroxide (slaked lime) until saturated and then filter to get calcium hydroxide solution (limewater)
• limestone is calcium carbonate
• quicklime is calcium oxide
• slaked lime is calcium hydroxide
• limewater is calcium hydroxide solution
• exothermic is the exit of heat
• endothermic is the entry of heat
• chemical symbols:

  calcium carbonate = CaCO3

  calcium oxide = CaO

  calcium hydroxide = Ca(OH)2

  limewater = Ca(OH)2
• uses of limestone:

  making concrete

  in statues

  stops soil getting too acidic

  neutralises acid in soil because limestone is alkaline
• number of moles = mass / formula mass (Ar or Mr)
• Empirial formula:

  1. calculate mols using mols = mass/Ar
  2. divide each by the smallest number of mols
  3. use ratio to find formula of compound
• empirial formula or simplest formula is used to find the formula of a compound
• what is thermal decomposition?

  breaking down using heat
• simplest or empirical formula shows simplest ratio while molecular formulas is what is actually there in the chemical
• molecular formula:

  1. calculate Mr of empirical formula
  2. divide the molecular mass given by the Mr
  3. multiply each atom in the empirical formula by the answer above
• Other metal carbonates also decompose thermally to form the metal’s oxide and carbon dioxide
• Quarrying for limestone: Advantages

  • Provides materials for the construction industry
  • More local jobs.
  • Creates more wealth for the community
  • Build better road systems
• Quarrying for limestone: Disadvantages

  • Dust from lorries and explosions
  • Spoils the landscape
  • Noise pollution
  • Destruction of habitats
• Iimestone heated into quicklime

  CaCO3 --> CaO + CO2
• water added to quicklime into slaked lime

  CaO + H2O --> Ca(OH)2
• slaked lime add carbon dioxide into limestone

  Ca(OH)2 + CO2 --> CaCO3 + H2O