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THMG123 – Chemical Reactions


In this episode, Bob explores the different chemical reactions you may encounter and how they affect our response.

Complete Show Notes

1:15 Overview of Chemical Reactions

  • Chemical reactions are covered in the yellow section of NFPA 704
  • Chemical reactions can liberate:
    • Light
    • Make or take heat
    • New products
    • New gasses
    • Precipitates
    • Water
    • Flammables
  • Nothing is lost or gained in terms of atoms, but energy is redirected
  • This redirection takes place by moving or altering the bonds and placement of electrons in the atoms (species)
  • Physical “reactions” are different from chemical changes (i.e. air conditioners vs. ice packs)

4:40 Rate of Change

  • Some take less than a second, while others take thousands of years (i.e. fossilization or decay half-lives of radiation)
  • Several factors determine rate of change:
    • Temperature
      • If you raise the temperature, the molecules bounce around more to create more energy
      • For example, think of the SADT of organic peroxides – they have to be kept in a fridge and mixed in an ice bath
    • Concentration
      • If there are a lot of molecules, there’s a good chance they’ll collide and cause a reaction – referred to as the collision theory
      • This is why adding a few drops of something to a test tube is slow to react, while adding more drops makes things happen a bit more quickly
    • Pressure
      • Changes the density of the molecules in the volume, therefore increasing the chances they’ll collide
      • Particularly significant for gasses

8:50 Equilibrium

  • When we have a reaction, the event goes on until the product reaches equilibrium
  • Process of reaching equilibrium:
    • Two reactants come together to react and make a product
    • In limited quantities, the product will go back to being a reactant
    • This will go on until there’s less and less of the reactants going back and forth
    • At this point, you’ve reached equilibrium
  • Catalysts and inhibitors cause reactions to speed up or slow down
  • Example:
    • If you fill a room with 2 parts hydrogen and 1 part oxygen, nothing happens
    • If you light a match, you’ll get an explosion
    • If you add some palladium to the room, the reaction will slow down significantly
  • Put simply, these two things change the activation energy of the reaction

12:15 Combination Reactions

  • Taking two or more reactants and making one product – like sodium chloride (table salt) from sodium and chlorine

13:00 Decomposition Reactions

  • The opposite of combination reactions where products are broken apart
  • For example, if we take water and add the right amount of electricity (electrolysis), we can break the water down into hydrogen and oxygen

15:15 Single Displacement Reactions

  • In this reaction, one atom that’s more “active” than another is kicked out of the molecule
  • For example, when zinc reacts with copper sulfate, it kicks the copper sulfate out of the party
  • These reactions produce a lot of heat

16:35 Double Displacement Reactions

  • In this reaction, two atoms are kicked out of the molecule – referred to as a metathesis reaction
  • Usually takes place in a solution in one of two types:
    • Precipitation – makes a solid from two liquids and is usually accompanied by heat and a gas
    • Water production – the operation we perform when doing acid and base neutralization

18:25 Combustion Reactions

  • Fire!

18:45 Reduction Reactions

  • In these reactions, electrons are exchanged
  • We find reduction reactions in combustion, rusting, photosynthesis, batteries, respiration, and more

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  1. Hey guys, just listened to podcast 123. I’d love to hear more about chemical reactions. Street smart stuff is always great.


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