Chemical Reactions Lesson

The law of conservation of mass states that in a closed system, the total mass remains constant during a chemical reaction. This happens because atoms, which are the building blocks of matter, are neither created nor destroyed during the reaction. Instead, they are rearranged to form new substances.

​Law of Conservation of Mass

​This is why we balance equations!

​A balanced equation has the same number of each atom on each side of the equation.

​Reactants - what you start with

Products - what you end up creating

Signs that a Chemical Reaction Happened

• An unexpected color change

• Gas is formed (bubbles!)

• Change in temperature

  • exothermic - released heat

  • endothermic - absorbed heat

• New smell

• Sound or light is produced

• A precipitate is formed →

When you predict a product, it is important to know how to write a formula

​You have rules and flowcharts to help you write the names and formulas for both ionic and covalent compounds. Here are a few things to remember:

1. Is the first element a metal? If it is, then you have to look at the charges on the ions. If it is not, then you will use the prefixes.

2. If the first element is a metal, is it a transition metal, or a metal like Pb or Sn? If so, you will need to remember in the name the charge is a Roman numeral in ( ).

3. No matter what type of compound it is, change the ending of the second element to IDE, unless the second part is a polyatomic ion.

4. Use your polyatomic ion charts to find the name, formula and charge on polyatomic ions. Do not change the name or formula of a polyatomic ion.