Balancing Chemical Equations notes for p. 8-10

Law of Conservation of Mass Balanced Equation Atoms can’t be created or destroyed Law of Conservation of Mass 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).

Counting Atoms 2H2 + O2  2H2O Subscript: (numbers below) Reactants  product Subscript: (numbers below) indicates how many atoms of an element. Coefficient (numbers in front) Indicates how many molecules/moles of a compound (multiplies the number of atoms of each element in the compound)

Chemical Formula Counting up Atoms

Let’s Practice NH3 NaCl _____ atoms of Nitrogen _____ atoms of Hydrogen _____ molecules/moles of NH3 NaCl _____ atoms of Sodium _____ atoms of Chlorine _____ molecule/moles of NaCl

Practice NH3 NaCl __1___ atoms of Nitrogen __3___ atoms of Hydrogen __1__ molecules/moles of NH3 NaCl __1___ atoms of Sodium __1___ atoms of Chlorine __1___ molecule/moles of NaCl

Practice Again 8NaCl 3NH3 Ca(NO3)2 _____ atoms of Sodium _____ atoms of Chlorine _____ molecule/moles of NaCl 3NH3 ____ atoms of Nitrogen ____ atoms of Hydrogen ___ molecule/moles of NH3 Ca(NO3)2 _____ atoms of Calcium _____ atoms of Nitrogen _____ atoms of Oxygen _____molecule/moles of Ca(NO3)2

Practice Again 8NaCl 3NH3 Ca(NO3)2 __8___ atoms of Sodium __8___ atoms of Chlorine __8___ molecule/moles of NaCl 3NH3 __3__ atoms of Nitrogen __9__ atoms of Hydrogen __3_ molecules/moles of NH3 Ca(NO3)2 ___1__ atoms of Calcium ___2__ atoms of Nitrogen ___6__ atoms of Oxygen ___1__molecule/moles of Ca(NO3)2 What if there is a coefficient of 2 in front of Ca(NO3)2 ?

More Practice SO2 + 3H2O _____ atoms of Sulfur _____ atoms of Hydrogen _____ atoms of Oxygen _____ molecule/moles of SO2 _____ molecules of H2O

More Practice SO2 + 3H2O __1___ atoms of Sulfur __6___ atoms of Hydrogen __5___ atoms of Oxygen __1___ molecule/moles of SO2 __3___ molecules of H2O

Let’s Step It Up a Little 2NH4NO3 + 3H2S _____ atoms of Nitrogen _____ atoms of Hydrogen _____ atoms of Oxygen _____ atoms of Sulfur _____ molecule/moles of NH4NO3 _____ molecule/moles of H2S

Let’s Step It Up a Little 2NH4NO3 + 3H2S __4___ atoms of Nitrogen __14___ atoms of Hydrogen __6___ atoms of Oxygen __3___ atoms of Sulfur __2___ molecule/moles of NH4NO3 __3___ molecule/moles of H2S

You Must Be Joking! 2Na2CO3 + 3CO2 + 4NaCl + Mg(NO3)2 _____ atoms of Sodium _____ atoms of Carbon _____ atoms of Oxygen _____ atoms of Chlorine _____ atoms of Nitrogen _____ atoms of Magnesium _____molecules/moles of Na2CO3 _____ molecule/moles of CO2 _____ molecule/moles of NaCl _____ molecule/moles of Mg(NO3)2

You Must Be Joking! 2Na2CO3 + 3CO2 + 4NaCl + Mg(NO3)2 __8___ atoms of Sodium __5___ atoms of Carbon __18___ atoms of Oxygen __4___ atoms of Chlorine __2___ atoms of Nitrogen __1___ atom of Magnesium __2___molecules/moles of Na2CO3 __3___ molecule/moles of CO2 __4___ molecule/moles of NaCl __1___ molecule/moles of Mg(NO3)2

® O + C O C O O Shows the reaction to form carbon dioxide C + O2 ® CO2 This equation is already balanced What if it isn’t already?

® O + C C O O Shows the reaction to form carbon monoxide C + O2 ® CO We need one more oxygen in the products. Can’t change the formula, because it describes what is produced. Remember, oxygen is a diatomic molecule.

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

C C ® O O + O C C O Must have started with two C 2 C + O2 ® 2 CO

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. If you change the formula you are describing a different reaction. H2O is a different compound than H2O2 Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not.

Example H2 + O2 ® H2O Make a table to keep track of where you are at

Example H2 + O2 ® H2O R P 2 H 2 2 O 1 Need twice as much O in the product

Example H2 + O2 ® 2 H2O R P 2 H 2 2 O 1 Changes the O

Example H2 + O2 ® 2 H2O R P 2 H 2 2 O 1 2 Also changes the H

Example H2 + O2 ® 2 H2O R P 2 H 2 4 2 O 1 2 Need twice as much H in the reactant

Example 2 H2 + O2 ® 2 H2O R P 2 H 2 4 2 O 1 2 Recount

Example 2 H2 + O2 ® 2 H2O R P 4 2 H 2 4 2 O 1 2 The equation is balanced, has the same number of each kind of atom on both sides

Example R P 4 2 H 2 4 2 O 1 2 2 H2 + O2 ® 2 H2O This is the answer Not this

Examples CH4 + O2 ® CO2 + H2O AgNO3 + Cu ® Cu(NO3)2 + Ag Mg + N2 ® Mg3N2 P + O2 ® P4O10 Na + H2O ® H2 + NaOH

Examples CH4 + 2O2 ® CO2 + 2H2O 2AgNO3 + Cu ® Cu(NO3)2 + 2Ag 3Mg + N2 ® Mg3N2 4P + 5O2 ® P4O10 2Na + 2H2O ® H2 + 2NaOH