Because of the principle of the Because of the principle of the

conservation of matterconservation of matter, ,

an an equation must be equation must be balancedbalanced..

It must have the same It must have the same number of atoms of the number of atoms of the same kind on both sides.same kind on both sides.

Lavoisier, 1788Lavoisier, 1788

Chemical EquationsChemical Equations

Scientists know that there Scientists know that there must be the same number must be the same number

of atoms on each side of the of atoms on each side of the arrow.arrow.

To balance the chemical To balance the chemical equation, you must add equation, you must add

COEFFICIENTS to the COEFFICIENTS to the different parts of the different parts of the

equation.equation.

Step # 1Step # 1

Determine the number of atoms for each Determine the number of atoms for each element.element.

Determine the number of atoms Determine the number of atoms for each element.for each element.

Mg + OMg + O2 2 MgOMgO

Determine the number of atoms Determine the number of atoms for each element.for each element.

Mg + OMg + O2 2 MgOMgO

1 Magnesium 1 Magnesium 1 Magnesium1 Magnesium

2 Oxygen2 Oxygen 1 Oxygen 1 Oxygen

Try to add coefficients to the Try to add coefficients to the equation to get the same number of equation to get the same number of

atoms on each side.atoms on each side.

Mg + OMg + O2 2 MgOMgO

1 Magnesium 1 Magnesium 1 Magnesium1 Magnesium

2 Oxygen2 Oxygen 1 Oxygen 1 Oxygen

2

Recount the atoms after adding Recount the atoms after adding a coefficient.a coefficient.

Mg + OMg + O2 2 MgOMgO

1 Magnesium 1 Magnesium 2 Magnesium2 Magnesium 2 Oxygen2 Oxygen 2 Oxygen 2 Oxygen

Still out of balance… Still out of balance…

2

Add a coefficient to the other Add a coefficient to the other sideside

Mg + OMg + O2 2 MgOMgO

1 Magnesium 1 Magnesium 2 Magnesium2 Magnesium 2 Oxygen2 Oxygen 2 Oxygen 2 Oxygen

Recount again… Recount again…

22

Recount the atoms…Recount the atoms…

Mg + OMg + O2 2 MgOMgO

2 Magnesium 2 Magnesium 2 Magnesium2 Magnesium 2 Oxygen2 Oxygen 2 Oxygen 2 Oxygen

It’s balanced!!!It’s balanced!!!

22

Types of reactionsTypes of reactions

SynthesisSynthesis DecompositionDecomposition Single replacementSingle replacement Double replacementDouble replacement CombustionCombustion

Try this oneTry this one

HH22OO22 H H22O + O + OO22

ProblemsProblems

Remember, count the atoms firstRemember, count the atoms first Add coefficients to balance one of the Add coefficients to balance one of the

atoms firstatoms first Recount atomsRecount atoms Keep working the coefficients until atoms Keep working the coefficients until atoms

are balancedare balanced

ProblemsProblems Na + Na + MgFMgF22 NaF + NaF + MgMg

ProblemsProblemsMg +Mg + HCl HCl MgClMgCl22 + + HH22

ProblemsProblems HH22 + + OO22 HH22OO

ProblemsProblemsMgCOMgCO33 + + NaF NaF NaNa22COCO33 + + MgF MgF22

SolutionsSolutions

1.1. 2 Na + MgF2 Na + MgF22 2 NaF + Mg 2 NaF + Mg

2.2. 2 Mg + 4 HCl 2 MgCl2 Mg + 4 HCl 2 MgCl22 + 2 H + 2 H22

3.3. 2H2H22 + O + O22 2H 2H22OO

4.4. MgCOMgCO33 + 2NaF + 2NaF NaNa22COCO33 + +

MgFMgF22

ChallengeChallenge

COCO22 + H + H22O O CC66HH1212OO66 + O + O22

Challenge solutionChallenge solution

6 CO6 CO22 + 6 H + 6 H22O CO C66HH1212OO66 + 6 O + 6 O22