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Chemical Reactions

Chemical Reactions. Five Types of Chemical Reactions:. 1. Combustion. 2. Synthesis. 3. Decomposition. 4. Single Displacement. 5. Double Displacement. Evidence that a chemical reaction has taken place?. Colour / Odour Change. Formation of a gas or solid. Difficult to reverse.

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Chemical Reactions

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  1. Chemical Reactions Five Types of Chemical Reactions: 1. Combustion 2. Synthesis 3. Decomposition 4. Single Displacement 5. Double Displacement

  2. Evidence that a chemical reaction has taken place? • Colour / Odour Change • Formation of a gas or solid • Difficult to reverse • Release/Absorption of Energy (heat)

  3. 1. Combustion Reactions • More commonly known as burning • Easily identified (release of heat) • For combustion 3 things need to be present: • Fuel • Oxygen • Heat

  4. Rocket Fuel: 2 H2(l) + O2(l) 2 H2O(g) + Heat • Sulphur (in gasoline): S(s) + O2(g) SO2(g) + Heat 1. Combustion Reactions

  5. Common OxidesResulting from Combustion Reactions

  6. A + B AB + 2. Synthesis Reactions • combination of two or more simple substances combining to form a more complex substance.

  7. Mg(s) + O2(g) MgO Synthesis of Magnesium Oxide 2 2

  8. Synthesis Reactions: C(s) + O2(g) CO2(g) S(s) + O2(g) SO2(g) Other Examples

  9. AB A + B + 3. Decomposition Reactions • Breaking down large, complex molecules or ionic compounds into smaller, simpler entities.

  10. H2O2(l) O2(g) + H2O(l) Decomposition of Hydrogen Peroxide 2 2

  11. A + BC AC + B 4. Single Displacement • reaction of an element with a compound that produces a new element and new compound.

  12. Single Displacement of Zinc and Chlorine HCl(aq) + Zn(s)  H2(g) + ZnCl2(aq) 2

  13. Chemical Reactions in Solution • SOLUTE – is a pure substance (usually lesser in quantity) that is dissolved in another pure substance called the “SOLVENT” • AQUEOUS SOLUTION – a solution in which water is the solvent (aqua – meaning water).

  14. Solubility • Solutions are homogenous mixtures of solutes and solvents. • Solubility is the measure of how much of the solute can possibly dissolve in a known amount of solvent. If a substance has high solubility in water, it has a subscript of (aq). However, if it isn’t very soluble it will start to precipitate out and will have a (s) subscript for solid.

  15. Use a Solubility Table • Is calcium hydroxide soluble? • Is sodium flouride soluble? • What about lead (II) Iodide?

  16. AB + CD AD + CB 5. Double Displacement • reaction of two compounds, where the positive and negative ions in their respective compounds switch places to form two new compounds. This can only happen with ionic compounds

  17. Double Displacement A double displacement reaction only occurs if one of the following three results are seen: • a precipitate is formed • a gas is produced • a change of pH occurs (a neutralization reaction) ** If the products are both soluble then the reaction is NR (no reaction)

  18. Double Displacement of Lead and Potassium Pb(NO3)2(aq) + KI(aq)  PbI2(s) + KNO3(aq) 2 2 Precipitate: A solid that is formed as a result of the chemical reaction of two aqueous solutions.

  19. More Examples • FeCl3(aq) + Na2(SO4)2(aq) → ? NR – both are soluble • HCl(aq) + LiOH(aq) →? pH change – neutralization reaction, products are LiCl & H2O • 2HNO3(aq)+ K2CO3(aq)→ CO2(g)+H2O(l) + 2 KNO3(aq) gas produced – therefore double displacement

  20. Percentage Composition Composition of Common Alloys

  21. Percent Composition • Percentages are calculated by weight How much gold (in grams) is there in 10g sample of 18K yellow gold where the % composition is 75% Au? Answer: mass of Au = (75% / 100) x 10g = 7.5 g Therefore there is 7.5 g of pure gold in a 10g sample of 18K yellow gold.

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