Chemical Reactions

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  • Created by: Em
  • Created on: 01-06-16 08:07

Combination & Decomposition Reactions

Combination/Synthesis Reactions

  • These reactions occur when 2 or more simpler substances react to form 1 more complex product 
  • For example magnesiums (Mg) + oxygen (O) --> magnesium oxide (MgO)

Decomposition Reactions

  • These reactions occur when one substance breaks down into 2 or more simpler substances 
  • For example, copper carbonate --> copper oxide + carbon dioxide 
  • If heat is used to break down the compound, it's thermal decomposition
  • If an electric current is used to break down the compound, it's electrolysis 
  • If a catalyst is used to break down a compound it's catalytic decomposition 


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Combustion Reactions

Combustion Reactions

  • These reactions occur when a reactant is micedd with oxygen and the reaction releases light/heat energy

Complete Combustion

  • Complete combustion is a reaction where there is lots of oxygen present 
  • Carbon dioxide and water are produced from this reaction 
  • Light and heat are produced as well

Incomplete Combustion

  • This reaction occurs when there is a limited supply of oxygen 
  • Carbon monoxide and water are the products of this type reaction
  • Light and heat are produced as well 
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Displacement Reactions

Displacement Reactions

  • These reactions happen when a more reactive element replaces a less reactive element from its compound 
  • For example, zinc + copper sulphate --> zinc sulphate + copper 
    • Zinc is more reactive than copper, so it replaces copper 
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Acid Reactions

Acid Reactions

  • There are 3 types of acid reactions:
    • Acid + alkali
    • Acid + metal 
    • Acid + metal carbonate
  • All acid reactions produce a metal salt and another product (either water, carbon dioxide or hydrogen gas)

Acid + Alkali

  • This is also known as a neutralisation reaction 
  • A salt and water are the products of this reaction 
  • For example, nitric acid + magnesium oxide --> magnesium nitrate + water 

Acid + Metal 

  • Salt and hydrogen gas are the products of this reaction 
  • For example, magnesium + sulphuric acid --> magnesium sulphate + hydrogen (gas) 
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Acid Reactions

Acid + Metal Carbonate 

  • Salt, water and carbon dioxide are the products of this reaction
  • For example, sodium carbonate + hydrochloric acid --> sodium chloride + carbon dioxide + water 

How to work out the salt formed:

  • Hydrochloric acid - Chloride
  • Sulfuric acid - Sulfate 
  • Nitric acid - Nitrate 
  • Ethanoic acid - Ethanoate 
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Precipitate Reactions

Precipitate Reactions

  • This reaction occurs when 2 soluble salt solutions react to form a precipitate (solid)
  • The solid that is formed is insoluble (doesn't dissolve) 
  • If there is an (aq) by an element, it means they break up into their ions
  • If there's a (s) by an element, it means it's a solid and is insoluble 
  • For example, potassium bromide + silver nitrate --> silver bromide(s) + potassium nitrate(aq)
  • You can figure out which products are (aq) and (s) by using the solubility rules
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Reaction Rates

Reaction Rates

  • For a chemical reaction to occur, particles must collide in the right orientation
  • The particles also need to collide with enough energy to overcome activation energy (an energy level that can break bonds)
  • The reaction rate is how fast a chemical reaction occurs
  • There are several ways to increase the reaction rate:


  • Refers to the amount of reacting particles per volume 
  • Concentrated solutions have a higher number of reacting particles per volume, dilute solutions have less per volume
  • When the concentration is higher the reaction rate is quicker because the particles collide more often per second, so the reaction happens faster
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Reaction Rates


  • When the temperature is higher the reaction rate is faster because the particles are moving quicker, therefore they have more kinetic energy to collide more
  • The particles will collide more and will have more energy to overcome activation energy, this leads to a faster reaction rate

Surface Area 

  • Breaking a solid into smaller pieces or grinding it into a powder will allow more surface area for the particle to react with, resulting in a faster reaction rate


  • A substance that speeds up the reaction bu is not used in the reaction
  • A catalyst lowers the activation energy needed for a reaction by putting reactants in the right orientation
  • By lowering the activation energy more particles and collisions will have the energy needed to overcome activation energy and react
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