Chemical Reactions Five Types of Chemical Reactions 1

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 l Formation l Difficult of a gas or solid to reverse l Release/Absorption of Energy (heat)

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

1. Combustion Reactions l Rocket Fuel: 2 H 2(l) + O 2(l) l Sulphur 2 H 2 O(g) + Heat (in gasoline): S(s) + O 2(g) SO 2(g) + Heat

Common Oxides Resulting from Combustion Reactions Combustion Situation Element in Reactant Common Oxide Coal in a coal-fired electricity generator carbon CO 2 Burning of rocket fuel Hydrogen H 2 O (g) Commercial production of sulphuric acid Sulphur SO 2 (g) Lightning strikes and volcanoes Nitrogren NO 2 (g)

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

Synthesis of Magnesium Oxide 2 Mg(s) + O 2(g) 2 Mg. O

Other Examples l Synthesis Reactions: C(s) + O 2(g) CO 2(g) S(s) + O 2(g) SO 2(g)

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

Decomposition of Hydrogen Peroxide 2 H 2 O 2(l) O 2(g)2+ H 2 O(l)

4. Single Displacement • 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 2 HCl(aq) + Zn(s) H 2(g) + Zn. Cl 2(aq)

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 • 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 p. H occurs (a neutralization reaction) ** If the products are both soluble then the reaction is NR (no reaction)

Double Displacement of Lead and Potassium Pb(NO 3)2(aq) + 2 KI(aq) Pb. I 2(s) + 2 KNO 3(aq) Precipitate: A solid that is formed as a result of the chemical reaction of two aqueous solutions.

More Examples • Fe. Cl 3(aq) + Na 2(SO 4)2(aq) → ? NR – both are soluble • HCl(aq) + Li. OH(aq) → ? p. H change – neutralization reaction, products are Li. Cl & H 2 O • 2 HNO 3(aq)+ K 2 CO 3(aq)→ CO 2(g)+H 2 O(l) + 2 KNO 3(aq) gas produced – therefore double displacement

Percentage Composition Alloy Composition of Common Alloys % 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 18 K gold Au (75%) Ag (13%) Cu (12%) Harder and less malleable than 24 K gold

Percent Composition • Percentages are calculated by weight How much gold (in grams) is there in 10 g sample of 18 K yellow gold where the % composition is 75% Au? Answer: mass of Au = (75% / 100) x 10 g = 7. 5 g Therefore there is 7. 5 g of pure gold in a 10 g sample of 18 K yellow gold.