Chemical Equations

Lavoisier, 1788 Chemical Equations Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides.

Scientists know that there must be the same number of atoms on each side of the arrow.

To balance the chemical equation, you must add COEFFICIENTS to the different parts of the equation.

Step # 1 • Determine the number of atoms for each element.

Determine the number of atoms for each element. Mg + O2 MgO

Determine the number of atoms for each element. Mg + O2 MgO 1 Magnesium 1 Magnesium 2 Oxygen 1 Oxygen

2 Try to add coefficients to the equation to get the same number of atoms on each side. Mg + O2 MgO 1 Magnesium 1 Magnesium 2 Oxygen 1 Oxygen

2 Recount the atoms after adding a coefficient. Mg + O2 MgO 1 Magnesium 2 Magnesium 2 Oxygen 2 Oxygen Still out of balance…

2 Add a coefficient to the other side Mg + O2 MgO 1 Magnesium 2 Magnesium 2 Oxygen 2 Oxygen Recount again… 2

2 Recount the atoms… Mg + O2 MgO 2 Magnesium 2 Magnesium 2 Oxygen 2 Oxygen It’s balanced!!! 2

Types of reactions • Synthesis • Decomposition • Single replacement • Double replacement • Combustion

Try this one H2O2 H2O + O2

Problems • Remember, count the atoms first • Add coefficients to balance one of the atoms first • Recount atoms • Keep working the coefficients until atoms are balanced

Problems Na + MgF2 NaF + Mg

Problems Mg + HCl MgCl2 + H2

Problems H2 + O2 H2O

Problems MgCO3 + NaF Na2CO3 + MgF2

Solutions • 2 Na + MgF2 2 NaF + Mg • 2 Mg + 4 HCl 2 MgCl2 + 2 H2 • 2H2 + O2 2H2O • MgCO3 + 2NaF Na2CO3 + MgF2

Challenge CO2 + H2O C6H12O6 + O2

Challenge solution 6 CO2 + 6 H2O C6H12O6 + 6 O2

Chemical Equations