CHEMICAL REACTIONS

Chemical Equations  Chemical Equations are used to represent chemical reactions. Reactants  Products  Law of Conservation of Matter means matter cannot be created or destroyed during a chemical reaction.  We must balance chemical reactions (add coefficients) to comply with the law.

Chemical Equations (Cont)  Example: CH 4 +O 2  CO 2 +H 2 O Methane + Oxygen  Carbon + Water Dioxide ReactantsProducts1 – C 4 – H2 – H 2 – O3 – O

Balancing  Chemical reactions change the groupings of the atoms, but DO NOT create or destroy atoms, so there must be the same number of each type of atom on each side of the arrow. We must use coefficients to Balance a Chemical Equation

Balancing Chemical Equations 1.Determine the correct formula for each reactant and product by supplying the subscripts to the formulas. Once you write the correct formula, DO NOT change the subscripts. 2.Add coefficients in front of balanced formulas to give the same number and kind of atoms on both sides. Use the lowest possible ratio of coefficients.

Example  CH 4 +2 O 2  CO 2 +2 H 2 O  If I place a 2 in front of the O 2 and the H 2 O, then I end up with: ReactantsProducts1 – C4 – H4 – O

You Try this One  C 2 H 4 +O 2  CO 2 +H 2 O 2 – C – H – O - 3  C 2 H 4 + 3O 2  2CO 2 +2H 2 O 2 – C – H – O - 6

Another Example  C 3 H 6 +O 2  CO 2 +H 2 O 3 – C – H – O - 3  2 C 3 H O 2  6 CO 2 +6 H 2 O 6 – C – H – O – 18

You Try This One  What would the coefficients be for this reaction: PCl 5 +H 2 O  H 3 PO 4 +HCl  1, 4, 1, 5

Physical States  Symbols in parentheses after each formula: 1.Solid(s) 2.Liquid(l) 3.Gas(g) 4.Aqueous(aq) 1.Aqueous means dissolved in water. –Example: 2 H 2 O 2 (aq)  2 H 2 O (l)+O 2 (g)

Word Equations  Chemical Equations written out as words. This is a statement that describes the chemical equation in place of using symbols.  Steps: 1.Using the words, write the correct formulas in the correct locations. 2.Add the states of matter abreviations. 3.Balance the equation.

Words to watch for  States of matter – This is a symbol that is used to identify the state of matter for each substance in a reaction.  Gas, Liquid, Solid, Aqueous Gas (g) Liquid (l) Solid (s) may also be called a Precipitant (ppt) or a crystal (c) Aqueous (aq) means dissolved in water.

Example 1  Solid Zinc reacts with Hydrochloric Acid to produce Zinc Chloride and Hydrogen gas.  Zinc + Hydrochloric Acid  Zinc Chloride + Hydrogen  Zn (s) + HCl (aq)  ZnCl 2 (aq) + H 2 (g)  Zn(s) + 2 HCl (aq)  ZnCl 2 (aq) + H 2 (g)

You Try This One  Solid Calcium Oxide reacts with solid Aluminum to produce solid Aluminium Oxide and Calcium.  calcium oxide + aluminum → aluminum oxide + calcium  CaO (s) + Al (s)  Al 2 O 3 (s) + Ca (s)  3CaO (s) + Al (s)  Al 2 O 3 (s) + 3Ca (s)

Example 2  Aqueous Lead (II) Nitrate reacts with aqueous Sodium Sulfate to produce aqueous Sodium Nitrate and solid Lead (II) Sulfate.  Lead (II) Nitrate + Sodium Sulfate  Sodium Nitrate + Lead (II) Sulfate  Pb(NO 3 ) 2 (aq) + Na 2 SO 4 (aq) → NaNO 3 (aq) + PbSO 4 (s)  Pb(NO 3 ) 2 (aq) + Na 2 SO 4 (aq) → 2 NaNO 3 (aq) + PbSO 4 (s)

You Try This One  Sodium Phosphate and Copper (II) Sulfate react in water to produce aqueous Sodium Sulfate and solid Copper (II) Phosphate.  sodium phosphate + copper (II) sulfate → sodium sulfate + copper (II) phosphate  Na 3 PO 4 + CuSO 4 → Na 2 SO 4 + Cu 3 (PO 4 ) 2