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Chemical Equations

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What are they? Equations showing chemical change(s). Example: CH 4 + 2O 2 CO 2 + 2H 2 O **Law of Conservation of Mass: reactantsproducts In a chemical reaction, mass (atoms) cannot be created or destroyed.

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A closer look Mass is always conserved in a chemical reaction. CH 4 + 2O 2 CO 2 + 2H 2 O ReactantsProducts Carbon11 Hydrogen44 Oxygen44

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Most chemical equations give the physical states of the reactants and products: (s) solid (l) liquid (g) gas (aq) aqueous solution (dissolved in water) Ex: 2Mg(s) + O 2 (g) 2MgO(s) 2HgO(s) 2Hg(l) + O 2 (g)

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Common diatomic gases H 2 N 2 O 2 Cl 2 Br 2 I 2 F 2

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6 Common Types of Chemical Reactions: 1) Synthesis 2) Decomposition 3) Combustion 4) Single Replacement 5) Double Replacement 6) Oxidation Reduction (REDOX) Reaction

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Synthesis Reaction in which 2 or more reactants combine to form a new compound. A + B AB Examples: 2K(s) + Cl 2 (g) 2KCl(s) Fe(s) + S(s) FeS(s)

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Decomposition A single compound is broken down into 2 or more products AB A + B Examples: CaCO 3 (s) CaO(s) + CO 2 (g) 2H 2 O(l) 2H 2 (g) + O 2 (g) PbO 2 (s) Pb(l) + O 2 (g) 2HgO(s) 2Hg(l) + O 2

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Combustion (burning in presence of Oxygen) Oxygen gas (O 2 ) reacts with another substance to produce an oxide*, water, and heat. *The oxide is typically carbon dioxide. Examples: CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g) + heat C 3 H 8 (g) + 5 O 2 (g) 3 CO 2 (g) + 4 H 2 O(g) + heat

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Single Replacement One element replaces another element in a compound A + BC AC + B (a metal replaces a cation) AB + C AC + B (a nonmetal replaces an anion) Examples: Mg(s) + Zn(NO 3 ) 2 (aq) Mg(NO 3 ) 2 (aq) + Zn(s) 2K(s) + 2H 2 O(l) 2KOH(aq) + H 2 (g)

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You must follow the rules! NO REACTION

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The Activity Series of Metals A list of metals in order of decreasing reactivity. A reactive metal will replace any of the metals listed below it in the series. Examples: Mg(s) + AgNO 3 (aq) Mg(NO 3 ) 2 (aq) + Ag(s) Mg(s) + LiNO 3 (aq) No Reaction

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Halogen Activity Series

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Double Replacement An exchange of cations between two reacting compounds. This type of reaction typically occurs between 2 ionic compounds in aqueous solution. AB + CD AD + CB Example: AgNO 3 (aq) + KCl(aq) AgCl(s) + KNO 3 (aq)

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3 Types of Double Replacement Reactions 1. Precipitation Reaction -produces a precipitate (formation of a solid) -Example: K 2 CO 3 (aq) + BaCl 2 (aq) 2KCl(aq) + BaCO 3 (s) 2. Gas Production -produces a gas -Example: 2NaCN(aq) + H 2 SO 4 (aq) 2HCN(g) + Na 2 SO 4 (aq) 3. Neutralization Reaction -produces water and salt -Example: Ca(OH) 2 (aq) + 2HCl(aq) CaCl 2 (aq) + 2H 2 O(l)

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Oxidation Reduction (REDOX) Reactions Any reaction in which the oxidation states of atoms change Oxidation=loss of electron(s) Reduction=gain of electron(s) Example: 4Al (s) + 3O2 (g) 2Al2O3 (s) 4Al 4Al + 12 e - Al was oxidized 6O + 12 e - 6O O was reduced 00 +3 0 -2 0 +3 -2

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Assigning Oxidation States (aka Oxidation Number) Hypothetical charge use to indicate the degree of oxidation (loss of electrons) Rules in assigning oxidation states: 1) The oxidation state of a free element is zero (0). ex. O 2 (g), Ag (s) 2) The oxidation state of a monatomic ion is equal to its ionic charge. (ex. Na +, Cl -3 ) 3) H has an oxidation of +1 and oxygen has an oxidation state of -2 when they are present in most compounds. (Exceptions: Hydrogen is -1 in hydrides of metals such as LiH, and Oxygen is -1 in peroxides such as H 2 O 2.) 4) The sum of all oxidation states in a neutral molecule must be zero, and the sum of the oxidation states in an ion must be equal to the ions overall charge.

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Writing and Balancing Chemical Equations: Step 1) Determine the reactants, products and the physical states. Step 2) Write the unbalanced equation to summarize the word equation. Step 3) Use coefficients to balance each and every element EXCEPT H and O. Step 4) Use coefficients to balance the Hydrogens. Step 5) Use coefficients to balance the Oxygens.

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Example #1 Chlorine gas and potassium iodide solution react together to form potassium chloride and iodine gas. Cl 2 (g) + KI(aq) KCl(s) +I 2 (g) Cl 2 (g) + 2KI(aq) 2KCl(s) +I 2 (g) Write the equation: Balance the equation:

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Example #2 Aluminum hydroxide solution is heated and decomposed into a solid aluminum oxide and liquid water. Write the equation:Al(OH) 3 (aq) Al 2 O 3 (s) + H 2 O(l) Balance the equation2Al(OH) 3 (aq) Al 2 O 3 (s) + 3H 2 O(l)

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Example #3 Zinc and Lead (II) nitrate react to form zinc nitrate and Lead. Zn(s) + Pb(NO 3 ) 2 (s) Zn(NO 3 ) 2 (s) + Pb(s)

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Predicting Products while considering the Solubility Rules: Example: K 2 CrO 4 (s) + Ba(NO 3 ) 2 (s) KNO 3 (s) + BaCrO 4 (s)