SCH3U - Writing Chemical Equations 1 PDF

Writing Chemical Equations Types of Change Physical Change: A change when no new substance is formed. Examples: change of state; dissolve substances; cut or crush Chemical Change: A change when a new substance is formed because bonds break and new bonds form. Examples: Combustion; synthesis; d...

Writing Chemical Equations Types of Change Physical Change: A change when no new substance is formed. Examples: change of state; dissolve substances; cut or crush Chemical Change: A change when a new substance is formed because bonds break and new bonds form. Examples: Combustion; synthesis; decomposition; single displacement; double displacement; redox. Chemical Reaction: transforms elements and compounds into new substances 1. Chemical Equations: Shows the relative amounts of reactants and products On the left hand side of an equation are the reactants and on the right hand side of the equation are the products. Chemical equations can be written as: word, skeleton, and balanced chemical equations. 2. Word Equations – the reactants and products are written out with a “+” sign in between the reactants or products and an “→” in between the reactants and products. hydrogen gas + oxygen gas → water + energy 3. Skeleton Equation – converts the words to symbols and formulas H2(g)+ O2(g) → H2O(l) + 572 kJ Law of Conservation of Mass In any chemical reaction, mass is neither created nor destroyed. This is why you MUST balance your equation: in order to conserve matter. Eg) 2H2(g)+ O2(g) → 2H2O(l) + 572 kJ Balanced Thermochemical Equation – when the energy term is included in a balanced equation; follows the Law of Conservation of Energy. Law of Conservation of Energy – in any chemical reaction, energy is neither created nor destroyed. Factors Affecting the Rate of Chemical Reaction Temperature - ↑ temperature, ↑ rate of reaction Concentration - ↑ concentration, ↑ rate of reaction Surface Area - ↑ surface area, ↑ rate of reaction Addition of a Catalyst – add a catalyst, ↑ rate of reaction Type of Particle – the simpler the type of reactant, the faster the rate of reaction. Balancing Chemical Reactions Subscripts – (numbers on the lower right side of chemical symbol) in a correct formula tell the number of atoms in one molecules. Coefficients – (numbers in front of a formula) in a correctly balanced equation tell the number of molecules involved in a reaction.  There is a particular order that you can follow in balancing. It is the MINOH method. Often, balancing H and O will involve water on one side of the other. Also, look carefully for elements which occur in only one place on each side of the arrow. These should be balanced before examining elements that are spread over several compounds. Often either H or O will be spread out over several compounds. This is the one to leave to the last. *Remember, you cannot change a subscript to balance the equation, nor can you add in new compounds. Examples: Example 1: Given the following word equation, write the corresponding balanced skeletal equation: potassium sulfate + sodium hydroxide → potassium hydroxide + sodium sulfate K2SO4+ 2 NaOH → 2 KOH + Na2SO4 Example 2: Given the following skeletal equation, write the corresponding word equation: iron(III) nitrate + ammonium hydroxide → iron (III) hydroxide + ammonium nitrate  Example 3: Balance the following equations. Ca + 2HCl → CaCl2 + H2 2Fe2O3 → 4Fe + 3O2 2Na3PO4 + 3MgOH2 → 6NaOH + Mg3(PO4)2 C3H8 + 5O2 → 3CO2 + 4H2O 2C8H18+ 25O2 → 16CO2 + 18H2O How do you determine States of Matter? All chemical species have a phase or state – either solid (s), liquid (l), gas (g) or in an aqueous solution (aq). There are rules to determine which state the species is in, within the reaction. 1. Elements – check the periodic table Liquids: Mercury – Hg(l), Bromine – Br2(l) Gases: Hydrogen – H2, Nitrogen – N2, Oxygen – O2, Fluorine – F2, Chlorine – Cl2, noble gases Solids: all other elements 2. If you know you have a solution, write (aq) 3. All ionic compounds, unless they are in solution, are solids (s) 4. All acids are in solution (aq) 5. All molecular oxides are gases (g) – N2O4(g) Example 4 Write a balanced equation for each of the following: Aluminum + sulfuric acid → aluminum sulfate solution + hydrogen 2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g) Potassium chlorate potassium chloride + oxygen 2KClO3 (s) 2KCl(s) + 3O2(g) The combustion of acetylene gas (C2H2) forms carbon dioxide gas and water vapour. 2C2H2(g) + 5O2(g )→ 4CO2(g) + 2H2O(g)