A. Equations show:
1.the reactants which enter into a reaction.
2.the products which are formed by the reaction.
3.the amounts of each substance used and each substance produced. B. Two important principles to remember:
1.Every chemical compound has a formula which cannot be altered. 2.A chemical reaction must account for every atom that is used. This is an application of the Law of Conservation of Matter which states that in a chemical reaction atoms are neither created nor destroyed. C. Some things to remember about writing equations:
1.The diatomic elements when they stand alone are always written H2, N2, O2, F2, Cl2, Br2, I2 2.The sign, → , means "yields" and shows the direction of the action. 3.A small delta, (), above the arrow shows that heat has been added. 4.A double arrow, ↔ , shows that the reaction is reversible and can go in both directions. 5.Before beginning to balance an equation, check each formula to see that it is correct. NEVER change a formula during the balancing of an equation. 6.Balancing is done by placing coefficients in front of the formulas to insure the same number of atoms of each element on both sides of the arrow. Practice Balancing Equations
7.Always consult the Activity Series of metals and nonmetals before attempting to write equations for replacement reactions. 8.If a reactant or product is a solid, (s) is placed after the formula. 9.If a reactant or product is a gas, (g) is placed after it. 10.If a reactant or product is in water solution, (aq) is placed after it. 11.Some products are unstable and break down (decompose) as they are produced during the reaction. You need to be able to recognize these products when they occur and write the decomposition products in their places. Examples:
•H2CO3(aq) → H2O(l) + CO2(g)
Carbonic acid, as in soft drinks, decomposes when it is formed. •H2SO3(aq) → H2O(l) + SO2(g)
Sulfurous acid also decomposes as it is formed.