Chemical Equations Click here to see reactions

 Reactants → Products  Bonds broken → bonds formed  Atoms are not created or destroyed, but rearranged

 Word Equations – put equations in a word form Iron + oxygen → Iron (III) Oxide Hydrogen Peroxide → Water + Oxygen  Chemical Equations – typically we use chemical symbols and chemical formulas to write chemical equations. Fe + O 2 → Fe 2 O 3 This would be a skeleton equation and does not show the relative amounts of reactants and products nor their states.

 Symbols (p 708) are used to indicate the Physical State of a compound. (s) solid (l) liquid (g) gas (aq) aqueous – dissolved in water Fe (s) + O 2 (g) → Fe 2 O 3 (s)  Catalyst – speeds up the rate of a reaction, but is not used up. MnO 2 H 2 O 2 (aq) → H 2 O (l) + O 2 (g)

To balance a reaction, first write the skeletal equation then add only coefficients so that the equation obeys the law of conservation of mass. 1) Determine the correct formulae of the reactants and products. 2) Write the skeletal equation 3) Determine the number of atoms of each element on both sides to determine inequalities. 4) Balance one atom at a time using coefficients 5) Make sure all coefficients are at their lowest ratio Hints: *Leave polyatomic ions intact if they are on both sides *balance solo elements last *know the diatomic elements: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2

 Two or more substances combine to form a single substance  Reactants are usually two elements or two compounds  Examples: 2K (s) + Cl 2 (g) → 2KCl (s) 2S (s) + 3O 2 (g) → SO 2 (g)

 A single compound is broken down into two or more products.  Rapid decomposition reactions producing gas and heat (explosions!)  Examples: CaCO 3 (s) → CaO (s) + CO 2 (g) 2H 2 O (l) → 2H 2 (g) + O 2 (g)

Atoms of one element replace the atoms of a second element in a compound Mg (s) + 2HCl (aq) → MgCl 2 (aq) + H 2 (g) Whether one metal will displace another metal is determined by the relative activities of the two metals. In the following example, Mg must be more reactive than Cu for the reaction to take place. Mg (s) + Cu(NO 3 ) 2 (aq) → MgNO 3 (aq) + Cu (s)

1)Involve an exchange of positive ions between 2 reacting compounds – usually between 2 ionic compounds For a reaction to take place one of the following must occur: A precipitate must form Na 2 S (aq) + Cd(NO 3 ) 2 (aq)  CdS (s) + 2NaNO 3 (aq) A gas must be produced 2NaCn (aq) + H 2 SO 4 (aq)  2HCN (g) + Na 2 SO 4 (aq) Water is produced Ca(OH) 2 (aq) + 2HCl (aq)  CaCl 2 (aq) + H 2 O (l)

 Oxygen is often one of the reactants  CO 2 and water are often products  Examples: O 2 + CH 4  H CO 2 Cellular respiration

 There are three types of equations used to describe reactions in solution. 1) Molecular equation – shows the overall reaction, but not necessarily in the actual form in solution. Pb(NO 3 ) 2 (aq) + Na 2 SO 4 (aq)  PbSO 4 (s) + 2NaNO 3 (aq)

2) Complete Ionic Equation – represents all reactants or products that are soluble (aq) as ions. Pb NO Na + + SO 4 2-  PbSO 4 (s) +2Na + + 2NO 3 - 3) Net Ionic Equation – includes only those ions that react to form a solid or liquid. Pb 2+ + SO 4 2-  PbSO 4 (s) Spectator Ions - Na + and NO 3 - are spectator ions because they are not part of the reaction (do not form the solid or liquid) and remain dissolved.