chemical equations & Types of Chemical Reactions

1. chemical equations & Types of Chemical Reactions

2. Chemical Reactions • In a chemical reaction, one or more substances change into new/different substances • According to the Law of Conservation of Mass a skeleton chemical equation must be balanced by placing COEFFICIENTS in front of chemical formula(s) • NOTE – correct chemical formula can not be changed!!!!

3. Describing Chemical Reactions Lets look at a sample reaction: solid magnesium and hydrochloric acid react to form hydrogen gas and magnesium chloride solution • Equations are used to describe chemical reactions Word Equation Magnesium + hydrochloric acid hydrogen gas + magnesium chloride Chemical Equation Mg + 2 HCl H2 + MgCl2

4. Chemical Equation Mg + 2HCl H2 + MgCl2 Reactants Products

5. State Symbols • When looking at a chemical equation, we often do not know what state the reactants or products are in • State symbols are used to indicate the physical state of the chemicals in your equation at SATP. • (s) = Solid • (l) = Liquid • (g) = Gas • (aq) = aqueous, (dissolved in water)

6. State Symbols Balanced chemical equation with state symbols Mg(s) + 2 HCl(aq) H2(g) + MgCl2 (aq) Chemical equation Mg + 2HCl H2 + MgCl2

7. Although there are MILLIONS of possible chemical reactions, we are able to use patterns to identify/predict some general TYPES of reactions.

8. Types of Chemical Reactions • Synthesis • Decomposition • Single Displacement • Double Displacement • Combustion (complete & incomplete)

9. Synthesis Reactions The direct combination of 2 substances (elements or compounds) to form a compound. General equation: A + B → AB A and B can be elements or compounds, AB is a compound.

10. EXAMPLES OF SYNTHESIS Reactions: P4 (s) + 5 O2 (g)  2 P2O5 (s) 2 Na (s) + Cl2 (g) 2 NaCl (s) 2 Al (s) + 3 I2 (g)  2 AlI3 (s)

11. Special Type of Synthesis Reactions Metal oxide + water  base Na2O(s) + H2O(l)  2NaOH(aq) Non metal oxide + water  acid CO2(g) + H2O(l)  H2CO3(aq)

12. Decomposition Reactions - The splitting up of a larger molecule into simpler substances (elements or compounds). - often require heat, light or electricity  General Equation: AB→ A + B AB is a compound, A and B can be elements or compounds

13. Examples of Decomposition Rxns: Electrolysis: the decomposition of a compound by an electric current Electrolysis of water: 2 H2O (g)  2 H2 (g)+ O2 (g) Nitrogen triiodide decomposing: 2 NI3 (s)  N2 (g)+ 3 I2 (s) Breaking down of sugar C12H22O11 (s) 12 C (s) + 11 H2O (l)

14. Special Types of Decomposition Reactions • Carbonate  metal oxide + carbon dioxide • Na2CO3(s)  Na2O(s) + CO2(g) • Bicarbonate  metal oxide + carbon dioxide + water • NaHCO3(s)  Na2O(s) + CO2(g) +H2O(g) • Hydrate  compound + water • Al(NO3)3*5H2O(s)  Al(NO3)3(s) + 5H2O(g)

15. Single Displacement -one element takes the place of (displaces) another element in a compound -usually metals displace metals, and non metals displace non metals We use the metal activity series and halogen displacement series to help us predict single displacement reactions.

16. General equation: A+ BC → B + AC (A is a metal) or N + BC → B + CN (N is a non-metal) A, B, and N are elements/diatomic molecules. BC, AC and CN are compounds.

17. EXAMPLES of Single Displacement Reactions: 2 Mg (s) + CO2 (s)  C (s) + 2 MgO (s) Cu (s) + 2 AgNO3 (aq)  Cu(NO3)2 (aq) + 2 Ag (s) thermite (steel making) Fe2O3 (s) + 2 Al (s)  2 Fe (s) + Al2O3 (s)

18. Metals higher on the activity series table are stronger and end up with a partner!

19. Double Displacement -Involves the displacement of “partners” -the metal cationsin each reactant exchange places, elements in different compounds displace each other or exchange places. - a precipitate, a gas or a molecular compound is usually formed

20. General equation: AB + CD → AD+ CB A,C = metal cations (simple or polyatomic cations) B,D = non metallic anions (simple or polyatomic anions ) *Remember, metals can only switch with metals, and non-metals can only switch with non-metals!

21. Examples of double displacementReactions: 2 NaOH (aq) + Cu(NO3)2 (aq)  Cu(OH)2(s) + 2 NaNO3 (aq) Colour of the precipitate formed: light blue 2 NaI (aq) + Pb(NO3)2 (aq)  PbI2(s) + 2 NaNO3 (aq) Colour of the precipitate formed: yellow Note – We use the solubility rules to predict the subscript of new products formed

22. Combustion

23. A chemical reaction in which a substance (often hydrocarbons like propane (C3H8), methane (CH4) and kerosene (C10H22)) reacts rapidly with OXYGEN and releases heat and light energy.

24. The word equation for the COMPLETE COMBUSTION of a hydrocarbon: Δ Hydrocarbon +Oxygen → Carbon Dioxide + Water Vapour + Energy (light & heat) The general equation: CxHy+O2 →CO2 +H2O Eg. Propane in a BBQ Δ C3H8 (g) +5 O2(g)→3 CO2 (g)+4 H2O (g)

25. Incomplete Combustion • occurs when there is not enough O2 available for complete combustion • produces a mixture of CO, C, CO2, and H2O vapour depending on the oxygen supply available

26. Incomplete Combustion • Eg. Propane in a BBQ • C3H8 (g) + 3O2(g)→ CO2 (g)+ 4H2O (g) + C(s) +CO(g) • or • C3H8 (g) + 3O2(g)→ 4H2O (g) + C(s) + 2CO(g) • or • C3H8 (g) + 4O2(g)→ CO2 (g)+ 4H2O (g) + 2CO(g) • or • 2C3H8 (g) + 7O2(g)→ 8H2O (g) + 6CO(g) • or • C3H8 (g) + 2O2(g)→ 4H2O (g) + 3C(s)