Chemistry - Chemical Reactions


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This presentation was designed to meet the GCE 'O' Level Chemistry syllabus. The presentation will discuss on Combination, Combustion and Thermal Decomposition Reactions.

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Chemistry - Chemical Reactions

  1. 1. This presentation was produced by the Science department of TemasekSecondary School. Redistribution or reproduction of this resource isprohibited by copyright regulations.
  2. 2. Other ChemicalReactions
  3. 3. OTHER CHEMICAL REACTIONSYou will learn:• Combination reaction• Combustion reaction• Thermal decomposition
  4. 4. OTHER CHEMICAL REACTIONSElements can react in many ways to formnew compounds.The new compound formed will have totallydifferent properties from the startingelements.
  5. 5. Two elements can react to form a new compound ina combination reaction.Example 1:elementsodium(soft silverymetal)elementchlorine(greenish-yellowpoisonous gas)compoundsodiumchloride /common salt(white solid)Combination Reaction
  6. 6. Example 2Formation of copper chlorideelementcopper(reddish-brownsolid)elementchlorine(greenish-yellowpoisonous gas)compoundcopper chloride(green solid)
  7. 7. Combustion Reaction-When an element burns in oxygenExample 1:Burning ofmagnesium stripmagnesium + oxygen magnesiumoxidemagnesium
  8. 8. Combustion ReactionExample 2hydrogen + oxygen waterVideo: O2
  9. 9. Breaking up a Compound by Heating-Thermal DecompositionA compound may be broken down into simplersubstances. Heating is needed.New compound 1Copperoxide(black powderysolid)New compound 2Carbondioxide( colourless gas)Startingcompoundcopper carbonate(green powder)Video:
  11. 11. Writing Chemical EquationsYou need to know:1. The correct chemical formula of elements(metals e.g Na. Zn, Al, Mg etc)(gases: e.g Cl2, H2, O2 etc)2. Chemical formula of compounds (based on yourknowledge of valency)Example: chemical formula ofmagnesium chloride: Mg Cl2
  12. 12. Writing Chemical Equations3. Balancing the equationThis is to ensure that the no of atoms of eachelements is the same before and after thereaction.Example : Reaction of hydrogen and chlorine gasIs this chemical equation balanced?H2 + Cl2 2 HClH H ClCl ClHClH
  13. 13. Balancing Chemical Equations• All chemical equations must be balanced.• The number of atoms of an elementbefore and after the reaction must be thesame as the Law of conservation ofMatter states that:Atoms cannot be created nor destroyedin a chemical reaction.
  14. 14. How to Balance?H2 + Cl2 HClLeft hand side Right hand side2H atoms 2 Cl atoms 1H atom and 1 Cl atomThis equation is not balanced.
  15. 15. How to Balance?Balancing can be achieved by changing thenumber in front of the formulaH2 + Cl2 HClLeft hand side Right hand side2H atoms 2 Cl atoms 1H atom and 1 Cl atomH2 + Cl2 2 HClLeft hand side Right hand side2H atoms 2 Cl atoms 2H atoms and 2 Cl atomsBalanced!
  16. 16. More Examples
  17. 17. Writing Chemical EquationsCombination ReactionExample 1Sodium + chlorine sodium chlorideStep 1: Write the chemical formulaNa + Cl2 NaClStep 2Balancing to ensure atoms of each elements are the same on both side.
  18. 18. Why the need to balancechemical Equations?Law of Conservation of Matter:Atoms cannot be created nor destroyedStep 2: BalancingNa + Cl2 NaCl2 NaCl2 2 NaClFirst trynot balancedSecond tryBalanced!Na + Cl2Na + Cl2
  19. 19. Combination ReactionExample 2Copper + chlorine copper (II) chlorideStep 1: Write the chemical formulaCu + Cl2 CuCl2Step 2 :Balancing to ensure atoms of each elements are thesame on both sideCu + Cl2 CuCl2No need tobalance
  20. 20. Combustion ReactionExample 1Magnesium + oxygen magnesium oxideStep 1: Write the chemical formulaMg + O2 MgOStep 2 :Balancing to ensure atoms of each elements are the sameon both sideNeed tobalance?Mg + O2 MgO22
  21. 21. Combustion ReactionExample 2Hydrogen + oxygen waterStep 2 :Balancing to ensure atoms of each elements are the same onboth sideStep 1: Write the chemical formulaH2 + O2 H2ONeed tobalance?H2 + O2H2O22
  22. 22. Thermal Decomposition ReactionExample 1Copper copper + carbonCarbonate oxide dioxideStep 2 :Balancing to ensure atoms of each elements are the sameon both sideStep 1: Write the chemical formulaCu CO3 CuO + CO2Need tobalance?It is alreadybalanced
  23. 23. Summary• A chemical reaction can be representedby a word or chemical equation.• Word equations can be converted into achemical equations by using chemicalformulas.• All chemical equations must be balanced.
  24. 24. Part IIChemical Equations forReactions of Acids
  25. 25. Reactions of AcidsComplete the worksheet given on writingwords and chemical equationsNote:You must know the*chemical formula of acids and alkalis* chemical formula of the salts
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