Rates and Energy 1

Created by: Catherine
Created on: 22-04-13 20:15

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Rates and Energy 1
- How fast?
  - rate of reaction measures speed of reaction
    - amount of reactant used, or amount of product produced
- Collision Theory and Surface area
  - collision theory
    - reactions can only happen if particles collide
      - with enough energy to change into new substances
        minimum energy needed to react is activation energy
    - factors increasing collisions and energy
      - temperature
      - concentration of solutions
      - pressure of gases
      - surface area of solids
- Catalysts
  - change rate of chemical reactions
  - mainly used to speed up reactions
  - lower activation energy so more collisions result in reaction
  - solids used in powdered forms
    - this gives them large surface area to make them more effective
  - work only with one type of reaction
    - different catalysts needed for different reactions
- temperature
  - increases speed of particles
  - particles will collide with more energy
    - increases rate of reaction
  - small change in temp has large effect on reaction rate
  - we refrigerate and freeze food to slow down reactions
- concentration and pressure
  - more particles in the same volume
  - particles are closer together so collide more often
    - more particles in the same volume
  - increases pressure of gas puts more molecules in same volume
    - molecules collide more frequently
      - concentration and pressure
        particles are closer together so collide more often
        
        increases pressure of gas puts more molecules in same volume
        molecules collide more frequently
- Catalysts in action
  - economical because rarely need replacement
  - mainly used in industrial processes
  - some catalysts could cause harm to the envoironment
  - nanoparticles could provide efficient new catalysts
    - could further reduce energy costs
- Exothermic and Endothermic Reactions
  - exothermic
    - transfer energy to the surroundings
      - surroundings heat up
    - e.g. combustion
      - e.g. oxidation
        e.g. neutralisation
  - endothermic
    - take in energy from surroundings
      - surroundings cool down
        thermal decomposition
- reversible reactions
  - equal but opppositite energy transfers
  - exothermic in one direction and endothermic in other
    - e.g. blue copper sulfate crystals heated endothermic
      - water added is exothermic
- Using energy transfers
  - handwarmersand self heating cans use exothermic reactions
  - medical cold packs use endothermic reactions