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 Release/Absorption of Energy (heat)

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

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

Common Oxides Resulting from Combustion Reactions Combustion Situation Element in Reactant Common Oxide Coal in a coal-fired electricity generator carbon CO2 (g) Burning of rocket fuel Hydrogen H2O (g) Commercial production of sulphuric acid Sulphur SO2 (g) Lightning strikes and volcanoes Nitrogren NO2 (g)

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

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

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

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

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

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

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

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).

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.

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

5. Double Displacement AB + CD AD + CB 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 AB + CD AD + CB

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)

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.

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

Percentage Composition Alloy % Composition Property Brass Cu (70%) Zn (30%) Harder and more resistant to corrosion than copper Stainless Steel Fe (80%) Cr (18%) Ni (1%) Si (1%) More resistant to corrosion then iron 18K gold Au (75%) Ag (13%) Cu (12%) Harder and less malleable than 24K gold Composition of Common Alloys

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.