Chemical Equations Chemical change involves a reorganization of the atoms in one or more substances.

Chemical Equation A representation of a chemical reaction: CH 4 + O 2  CO 2 + H 2 O reactants products reactants products

Physical States When you see a chemical formula, often the formula is followed by a symbol in parentheses. For example: H 2 O(l) - the water is liquid H 2 O(l) - the water is liquid H 2 O(s) - the water is solid (ice) H 2 O(s) - the water is solid (ice) H 2 O(g)- the water is a gas (steam) H 2 O(g)- the water is a gas (steam) NaCl(aq) – means that the chemical is disolved in water. In this case it would be salt dissolved in water. NaCl(aq) – means that the chemical is disolved in water. In this case it would be salt dissolved in water.

The Magnificent 7 (diatomic molecules) Certain elements do not exist naturally as a single atom. They exist in pairs. Certain elements do not exist naturally as a single atom. They exist in pairs. So when writing out a chemical equation it is important to write the chemical formula to show that. So when writing out a chemical equation it is important to write the chemical formula to show that. The 7 are: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2 The 7 are: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2

Types of Reactions

Synthesis Reaction When two or more reactants come together to make one product. Also called Combination. When two or more reactants come together to make one product. Also called Combination. Example: Example: N 2 + H 2  NH 3 Note that diatomic molecules (Magnificent 7!) must be diatomic in their elemental form.

Decomposition Reaction When a single compound is broken down into two or more products When a single compound is broken down into two or more products Example: Example: H 2 O  H 2 + O 2

Single Displacement Reaction When an element and an ionic compound react and the element takes the place of its comparable ion When an element and an ionic compound react and the element takes the place of its comparable ion Metal element  takes positive ion’s place Metal element  takes positive ion’s place Nonmetal element  takes negative ion’ place Nonmetal element  takes negative ion’ place Examples: Examples: Mg + FeCl 3  MgCl 2 + Fe Br 2 + FeCl 3  FeBr 3 + Cl 2

Notice! The neutral atom joins the compound becoming a charged ion. The neutral atom joins the compound becoming a charged ion. The products MUST be electronically neutral. Since Mg becomes Mg +2, two Cl ions neutralize it. The products MUST be electronically neutral. Since Mg becomes Mg +2, two Cl ions neutralize it. The charge on the transition metal stays the same if it remains as an ion (iron is +3 charge in both the reactant and product) The charge on the transition metal stays the same if it remains as an ion (iron is +3 charge in both the reactant and product)

Double Displacement Reaction When two ionic compounds switch their partner ions. When two ionic compounds switch their partner ions. Positive goes with other negative and vice versa. Positive goes with other negative and vice versa. Switcheroo! Switcheroo! Example: Example: NaCl + MgBr 2  MgCl 2 + NaBr Pb(NO 3 ) 2 + Na 2 SO 4  NaNO 3 + PbSO 4

NaCl + MgBr 2  MgCl 2 + NaBr Pb(NO 3 ) 2 + Na 2 SO 4  NaNO 3 + PbSO 4 Notice! The reactants and products MUST be electronically neutral The reactants and products MUST be electronically neutral All ions keep their charge from reactants to products All ions keep their charge from reactants to products Do not get fooled into thinking that if there are a certain number atoms of an element in the reactants, there will be the same number in the products! Do not get fooled into thinking that if there are a certain number atoms of an element in the reactants, there will be the same number in the products! Polyatomic ions are very common in these types of reactions. Make sure you can spot them! Polyatomic ions are very common in these types of reactions. Make sure you can spot them!

Combustion Reactions When a hydrocarbon (something with C’s and H’s and sometimes O’s – organic molecule) reacts with Oxygen to form water and carbon dioxide and heat energy. When a hydrocarbon (something with C’s and H’s and sometimes O’s – organic molecule) reacts with Oxygen to form water and carbon dioxide and heat energy. Example: Example: CH 4 + O 2  CO 2 + H 2 O C 4 H 8 + O 2  CO 2 + H 2 O

Acid/Base reaction When an acid reacts with a base, water forms When an acid reacts with a base, water forms Acids produce H + in water Acids produce H + in water Bases produce OH - in water Bases produce OH - in water Example: Example: HNO 3 + KOH  HOH (or H 2 O) + KNO 3

What type of equation are each of the following reactions? P + O 2  P 2 O 5 C 3 H 5 O + O 2  CO 2 + H 2 O NH 4 NO 3  N 2 O + H 2 O Fe 2 O 3 + C  Fe + CO CO 2 + H 2 O  H 2 CO 3 CuNO 3 + Na 2 SO 4  Cu 2 SO 4 + NaNO 3

Check Your Answers P + O 2  P 2 O 5 Synthesis C 3 H 5 O + O 2  CO 2 + H 2 O Combustion NH 4 NO 3  N 2 O + H 2 O Decomposition Fe 2 O 3 + C  Fe + CO Single Displacement

Check Your Answers CO 2 + H 2 O  H 2 CO 3 Synthesis CuNO 3 + Na 2 SO 4  Cu 2 SO 4 + NaNO 3 Double Displacement