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Types of Reactions

Types of Reactions. Recall. A + B  C + D A and B are called reactants Means ‘yields’ C and D are called products. Evidence of chemical reactions. At least one of these should be obvious when a chemical reaction takes place:

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Types of Reactions

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  1. Types of Reactions

  2. Recall A + B C + D A and B are called reactants • Means ‘yields’ C and D are called products

  3. Evidence of chemical reactions At least one of these should be obvious when a chemical reaction takes place: • Color change - new substances might reflect different colors of light. • Heat change - the container may get hotter or colder. • Gas produced - bubbles or smoke may be observed. • Precipitate formed - an insoluble solid might form in a liquid.

  4. Types of reactions: • Synthesis – to build up • Decomposition – to break down • Single displacement – to replace one thing • Double displacement–to replace two things • Combustion – burn in presence of oxygen

  5. Synthesis • This reaction involves the combination of smaller atoms and/or molecules to produce a single product. Hydrogen chloride and ammonia yield ammonium chloride HCl + NH3 NH4Cl

  6. Decomposition • This reaction involves the splitting of a large molecule into elements or smaller molecules. • Sodium iodide  sodium and iodine • 2NaI  2Na + I2

  7. This chemical change involves an element and a compound as reactants. One element will DISPLACE the element from the compound. Mg + Ag(NO3)  Ag + Mg(NO3)2 Single Displacement

  8. Double Displacement • This reaction occurs when elements in different compounds displace each other or exchange places. Pb(NO3)2 + KI  PbI2 + K(NO3)

  9. Double Displacement • Neutralization of an acid and a base is also an example of a double displacement reaction. Acid + Base salt + water Ex. HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

  10. Combustion • This is generally a very quick reaction where one reactant is oxygen and the product formed is an oxide. Mg + O2 MgO C4H10 + O2 CO2 + H20 (complete combustion) • Incomplete combustion forms CO2, CO, C and H2O

  11. Metal oxides • Mg + O2 MgO(s) • MgO(s) + H2O(l)  Mg(OH)2(aq) pH scale measure the amount of hydrogen ions in the solution. pH scale: 0 (very acidic) 7(neutral) 14 (very basic)

  12. Indicators to measure pH • Litmus paper • Red litmus turns blue in a base • Blue litmus turns red in an acid • BTB(bromothymol blue) • Turns blue in a base • Turns yellow in an acid • Turns green in a neutral solution • PHTH (phenophthalein) • Turns colourless in an acid • Turns magenta pink in a base

  13. Non-metal oxide • Non-metal oxide and water form an acid. CO2 + H2O(l) H2CO3(aq) • Therefore this would lie under 7 on the pH scale (acidic environment)

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