Balancing Chemical Equations

BELL RINGER: Answer the question into your notebooks; make sure to write the examples, 1-8. Identify the following as an element or a compound: Na 2. NaF 3. Es 4. SiO 5. B 6. Ni 7. NaHCO3 8. MgCl2

Objectives Describe a chemical reaction by using a word equation and a formula equation. Relate the conservation of mass to the rearrangement of atoms in a chemical reaction Write and interpret a balanced chemical equation for a reaction, and relate conservation of mass to the balanced equation

What is a chemical equation? A chemical equation is a written symbolic representation of a chemical reaction. The reactant chemical(s) are given on the left-hand side and the product chemical(s) on the right-hand side. Reactants: substance(s) that participates in a chemical reaction Products: substance(s) that are produced during a chemical reaction

What is a chemical equation? Contin…. Here is an example of a chemical equation: C3H8 + O2  H2O + CO2 Reactants Products This reaction occurs when propane (C3H8) is burned in the presence of oxygen to produce water and carbon dioxide.

Conservation of Mass The law of conservation of mass states that no atoms can be created or destroyed in a chemical reaction, so the number of atoms that are present in the reactants has to balance the number of atoms that are present in the products. Reactants = Products

Write down the given chemical equation. C3H8 + O2 --> H2O + CO2

Step 1: Write down the number of atoms per each element that you have on each side of the equation Look at the subscripts next to each atom to find the number of atoms in the equation. C3H8 + O2 --> H2O + CO2 C = 3 H = 8 O = 2 reactants C = 1 H = 2 O = 3 products

Step 2: Pick an element that is not equal on both sides of the equation. Insert coefficients in front of the formula with that element. Balance one element at a time. Count atoms of each element frequently as you try different coefficients. In a chemical equation, you can change coefficients, but you must never alter the subscripts! C3H8 + O2 --> H2O + 3CO2 C = 3 H = 8 O = 2 reactants C = 1 3 H = 2 O = 3 7 products

Step 3: Continue adding coefficients to get the same number of atoms of each element on each side. In a chemical equation, you can change coefficients, but you must never alter the subscripts! C3H8 + 5O2 --> 4H2O + 3CO2 C = 1 3 H = 2 O = 3 7 products C = 3 H = 8 O = 2 reactants

Step 4: Check your answer! C3H8 + 5O2 --> 4H2O + 3CO2 C = 3 H = 8 O = 10 reactants C = 3 H = 8 O = 10 products

Practice Problems P4 + O2 P2O5 2. C3H8 + O2 CO2 + H2O 3. Ca2Si + Cl2 CaCl2 + SiCl4 4. Silicon (Si) reacts with carbon dioxide(CO2)to form silicon carbide,(SiC), and silicon dioxide (SiO2).