Balancing Chemical Equations

Balanced Equation Atoms can’t be created or destroyed Atoms can’t be created or destroyed Law of Conservation of Mass Law of Conservation of Mass All the atoms we start with we must end up with All the atoms we start with we must end up with A balanced equation has the same number of each element on both sides of the equation (reactant and product sides). A balanced equation has the same number of each element on both sides of the equation (reactant and product sides).

Counting Atoms 2H 2 + O 2  2H 2 O 2H 2 + O 2  2H 2 O Reactants  product Reactants  product Subscript: (numbers below) Subscript: (numbers below) indicates how many atoms of an element. indicates how many atoms of an element. Coefficient (numbers in front) Coefficient (numbers in front) Indicates how many molecules/moles of a compound Indicates how many molecules/moles of a compound (multiplies the number of atoms of each element in the compound) (multiplies the number of atoms of each element in the compound)

Chemical Formula Counting up Atoms

Let’s Practice NH 3 NH 3 _____ atoms of Nitrogen _____ atoms of Nitrogen _____ atoms of Hydrogen _____ atoms of Hydrogen _____ molecules/moles of NH 3 _____ molecules/moles of NH 3 NaCl NaCl _____ atoms of Sodium _____ atoms of Sodium _____ atoms of Chlorine _____ atoms of Chlorine _____ molecule/moles of NaCl _____ molecule/moles of NaCl

Practice NH 3 NH 3 __1___ atoms of Nitrogen __1___ atoms of Nitrogen __3___ atoms of Hydrogen __3___ atoms of Hydrogen __1__ molecules/moles of NH 3 __1__ molecules/moles of NH 3 NaCl NaCl __1___ atoms of Sodium __1___ atoms of Sodium __1___ atoms of Chlorine __1___ atoms of Chlorine __1___ molecule/moles of NaCl __1___ molecule/moles of NaCl

Practice Again 8NaCl 8NaCl _____ atoms of Sodium _____ atoms of Sodium _____ atoms of Chlorine _____ atoms of Chlorine _____ molecule/moles of NaCl _____ molecule/moles of NaCl 3NH 3 3NH 3 ____ atoms of Nitrogen ____ atoms of Nitrogen ____ atoms of Hydrogen ____ atoms of Hydrogen ___ molecule/moles of NH 3 ___ molecule/moles of NH 3 Ca(NO 3 ) 2 Ca(NO 3 ) 2 _____ atoms of Calcium _____ atoms of Calcium _____ atoms of Nitrogen _____ atoms of Nitrogen _____ atoms of Oxygen _____ atoms of Oxygen _____molecule/moles of Ca(NO 3 ) 2 _____molecule/moles of Ca(NO 3 ) 2

Practice Again 8NaCl 8NaCl __8___ atoms of Sodium __8___ atoms of Sodium __8___ atoms of Chlorine __8___ atoms of Chlorine __8___ molecule/moles of NaCl __8___ molecule/moles of NaCl 3NH 3 3NH 3 __3__ atoms of Nitrogen __3__ atoms of Nitrogen __9__ atoms of Hydrogen __9__ atoms of Hydrogen __3_ molecules/moles of NH 3 __3_ molecules/moles of NH 3 Ca(NO 3 ) 2 Ca(NO 3 ) 2 ___1__ atoms of Calcium ___1__ atoms of Calcium ___2__ atoms of Nitrogen ___2__ atoms of Nitrogen ___6__ atoms of Oxygen ___6__ atoms of Oxygen ___1__molecule/moles of Ca(NO 3 ) 2 ___1__molecule/moles of Ca(NO 3 ) 2 What if there is a coefficient of 2 in front of Ca(NO 3 ) 2 ? What if there is a coefficient of 2 in front of Ca(NO 3 ) 2 ?

More Practice SO 2 + 3H 2 O SO 2 + 3H 2 O _____ atoms of Sulfur _____ atoms of Sulfur _____ atoms of Hydrogen _____ atoms of Hydrogen _____ atoms of Oxygen _____ atoms of Oxygen _____ molecule/moles of SO 2 _____ molecule/moles of SO 2 _____ molecules of H 2 O _____ molecules of H 2 O

More Practice SO 2 + 3H 2 O SO 2 + 3H 2 O __1___ atoms of Sulfur __1___ atoms of Sulfur __6___ atoms of Hydrogen __6___ atoms of Hydrogen __5___ atoms of Oxygen __5___ atoms of Oxygen __1___ molecule/moles of SO 2 __1___ molecule/moles of SO 2 __3___ molecules of H 2 O __3___ molecules of H 2 O

Let’s Step It Up a Little 2NH 4 NO 3 + 3H 2 S 2NH 4 NO 3 + 3H 2 S _____ atoms of Nitrogen _____ atoms of Nitrogen _____ atoms of Hydrogen _____ atoms of Hydrogen _____ atoms of Oxygen _____ atoms of Oxygen _____ atoms of Sulfur _____ atoms of Sulfur _____ molecule/moles of NH 4 NO 3 _____ molecule/moles of NH 4 NO 3 _____ molecule/moles of H 2 S _____ molecule/moles of H 2 S

Let’s Step It Up a Little 2NH 4 NO 3 + 3H 2 S 2NH 4 NO 3 + 3H 2 S __4___ atoms of Nitrogen __4___ atoms of Nitrogen __14___ atoms of Hydrogen __14___ atoms of Hydrogen __6___ atoms of Oxygen __6___ atoms of Oxygen __3___ atoms of Sulfur __3___ atoms of Sulfur __2___ molecule/moles of NH 4 NO 3 __2___ molecule/moles of NH 4 NO 3 __3___ molecule/moles of H 2 S __3___ molecule/moles of H 2 S

You Must Be Joking! 2Na 2 CO 3 + 3CO 2 + 4NaCl + Mg(NO 3 ) 2 2Na 2 CO 3 + 3CO 2 + 4NaCl + Mg(NO 3 ) 2 _____ atoms of Sodium _____ atoms of Sodium _____ atoms of Carbon _____ atoms of Carbon _____ atoms of Oxygen _____ atoms of Oxygen _____ atoms of Chlorine _____ atoms of Chlorine _____ atoms of Nitrogen _____ atoms of Nitrogen _____ atoms of Magnesium _____ atoms of Magnesium _____molecules/moles of Na 2 CO 3 _____molecules/moles of Na 2 CO 3 _____ molecule/moles of CO 2 _____ molecule/moles of CO 2 _____ molecule/moles of NaCl _____ molecule/moles of NaCl _____ molecule/moles of Mg(NO 3 ) 2 _____ molecule/moles of Mg(NO 3 ) 2

You Must Be Joking! 2Na 2 CO 3 + 3CO 2 + 4NaCl + Mg(NO 3 ) 2 2Na 2 CO 3 + 3CO 2 + 4NaCl + Mg(NO 3 ) 2 __8___ atoms of Sodium __8___ atoms of Sodium __5___ atoms of Carbon __5___ atoms of Carbon __18___ atoms of Oxygen __18___ atoms of Oxygen __4___ atoms of Chlorine __4___ atoms of Chlorine __2___ atoms of Nitrogen __2___ atoms of Nitrogen __1___ atom of Magnesium __1___ atom of Magnesium __2___molecules/moles of Na 2 CO 3 __2___molecules/moles of Na 2 CO 3 __3___ molecule/moles of CO 2 __3___ molecule/moles of CO 2 __4___ molecule/moles of NaCl __4___ molecule/moles of NaCl __1___ molecule/moles of Mg(NO 3 ) 2 __1___ molecule/moles of Mg(NO 3 ) 2

C + O 2  CO 2 C + O 2  CO 2 This equation is already balanced This equation is already balanced What if it isn’t already? What if it isn’t already? C + O O  C O O

C + O 2  CO C + O 2  CO We need one more oxygen in the products. We need one more oxygen in the products. Can’t change the formula, because it describes what is produced. Can’t change the formula, because it describes what is produced. Remember, oxygen is a diatomic molecule. Remember, oxygen is a diatomic molecule. C + O  C O O

The other Oxygen must be used to make another CO The other Oxygen must be used to make another CO But where did the other C come from? But where did the other C come from? C + O  C O O O C

Must have started with two C Must have started with two C 2 C + O 2  2 CO 2 C + O 2  2 CO C + O  C O O O C C

Rules for balancing  Write the correct formulas for all the reactants and products  Count the number of atoms of each type appearing on both sides  Balance the elements (make them same amount on reactant and product sides) one at a time by adding coefficients (the numbers in front).  Check to make sure it is balanced.

Never! Change a subscript to balance an equation. Change a subscript to balance an equation. If you change the formula you are describing a different reaction. If you change the formula you are describing a different reaction. H 2 O is a different compound than H 2 O 2 H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not. 2 NaCl is okay, Na2Cl is not.

Example H 2 +H2OH2OO2O2  Make a table to keep track of where you are at

Example H 2 +H2OH2OO2O2  Need twice as much O in the product RP H O

Example H 2 +H2OH2OO2O2  Changes the O RP H O

Example H 2 +H2OH2OO2O2  Also changes the H RP H O

Example H 2 +H2OH2OO2O2  Need twice as much H in the reactant RP H O

Example H 2 +H2OH2OO2O2  Recount RP H O

Example H 2 +H2OH2OO2O2  The equation is balanced, has the same number of each kind of atom on both sides RP H O

Example H 2 +H2OH2OO2O2  This is the answer RP H O Not this

Examples CH 4 + O 2  CO 2 + H 2 O CH 4 + O 2  CO 2 + H 2 O AgNO 3 + Cu  Cu(NO 3 ) 2 + Ag AgNO 3 + Cu  Cu(NO 3 ) 2 + Ag Mg + N 2  Mg 3 N 2 Mg + N 2  Mg 3 N 2 P + O 2  P 4 O 10 P + O 2  P 4 O 10 Na + H 2 O  H 2 + NaOH Na + H 2 O  H 2 + NaOH

Examples CH 4 + 2O 2  CO 2 + 2H 2 O CH 4 + 2O 2  CO 2 + 2H 2 O 2AgNO 3 + Cu  Cu(NO 3 ) 2 + 2Ag 2AgNO 3 + Cu  Cu(NO 3 ) 2 + 2Ag 3Mg + N 2  Mg 3 N 2 3Mg + N 2  Mg 3 N 2 4P + 5O 2  P 4 O 10 4P + 5O 2  P 4 O 10 2Na + 2H 2 O  H 2 + 2NaOH 2Na + 2H 2 O  H 2 + 2NaOH