1. Law of Conservation of Mass In a chemical reaction, mass cannot be created or destroyed In a chemical reaction, mass cannot be created or destroyed Mass of the reactants is always equal to the mass of the products Mass of the reactants is always equal to the mass of the products Number of atoms in the reactants is always equal to the number of atoms in the products Number of atoms in the reactants is always equal to the number of atoms in the products Therefore in a chemical equation, there must be the same number of atoms of each element on each side  this is known as a “balanced chemical equation” Therefore in a chemical equation, there must be the same number of atoms of each element on each side  this is known as a “balanced chemical equation”

2. Steps to help balancing chemical equations: 1. Get yourself an unbalanced chemical equation - This may or may not be given; you MUST be able to determine the correct formulas for ALL of the compounds involved - i.e.: NaCl + BeF 2  NaF + BeCl 2 2. Figure out how many of each atom you have on your reactants side and your products side - Reactants: Na = 1, Cl = 1, Be = 1, F = 2 - Products: Na = 1, Cl = 2, Be = 1, F = 1 - Notice how Cl and F are not equal? We need to balance the equation. - We want each atom to be equal on each side of the reaction 3. Draw boxes around all the chemical compounds - This is to remind you to NEVER change anything inside the boxes (i.e.: subscripts). If you do, you will ALWAYS get the wrong answer - i.e.: NaCl + BeF 2  NaF + BeCl 2

3. Steps to help balancing chemical equations: 5. Write coefficients (numbers) in front of the boxes to the left in order to make the numbers of atoms to be equal on each side of the equation - i.e.: NaCl + BeF 2  NaF + BeCl 2 - The coefficients are multiplied to each atom in a compound - i.e. – place a 2 in front of NaCl to get 2NaCl; this means that we now have 2 Na’s and 2 Cl’s - Atoms with subscripts have the subscript multiplied - i.e. – if we placed a 2 in front of BeF 2 we would get 2 BeF 2 ; this means that we now have 2 Be’s and 4 F’s - NEVER CHANGE THE INITIAL SUBSCRIPT - This will ALWAYS give you the wrong answer - i.e. – Do not change BeF 2 to BeF 4 6.Use a pencil – you will have to use trial and error to get the final answer 2NaCl + BeF 2  2NaF + BeCl 2 2NaCl + BeF 2  2NaF + BeCl 2

4. Examples __ FeCl 3 + __ Be 3 (PO 4 ) 2  __ BeCl 2 + __ Fe(PO 4 ) __ FeCl 3 + __ Be 3 (PO 4 ) 2  __ BeCl 2 + __ Fe(PO 4 ) __ Ag(NO 3 ) + __ Li(OH)  __ Ag(OH) + __ Li(NO 3 ) __ Ag(NO 3 ) + __ Li(OH)  __ Ag(OH) + __ Li(NO 3 ) __CH 4 + __ O 2  __ CO 2 + __ H 2 O __CH 4 + __ O 2  __ CO 2 + __ H 2 O __ Mg + __Mn 2 O 3  __ MgO + __ Mn __ Mg + __Mn 2 O 3  __ MgO + __ Mn

5. Examples - Answers 2 FeCl 3 + Be 3 (PO 4 ) 2  3 BeCl 2 + 2 Fe(PO 4 ) 2 FeCl 3 + Be 3 (PO 4 ) 2  3 BeCl 2 + 2 Fe(PO 4 ) Ag(NO 3 ) + Li(OH)  Ag(OH) + Li(NO 3 ) Ag(NO 3 ) + Li(OH)  Ag(OH) + Li(NO 3 ) CH 4 + 2 O 2  CO 2 + 2 H 2 O CH 4 + 2 O 2  CO 2 + 2 H 2 O 3 Mg + Mn 2 O 3  3 MgO + 2 Mn 3 Mg + Mn 2 O 3  3 MgO + 2 Mn

6. But here’s the best part… If you understand how to balance equations instinctively, you don’t NEED to go through all the steps. The steps are just there to help you! If you understand how to balance equations instinctively, you don’t NEED to go through all the steps. The steps are just there to help you! Honestly, sometimes the best strategy for balancing equations is trial and error Honestly, sometimes the best strategy for balancing equations is trial and error Keep practicing and working on questions and it will get easier & easier Keep practicing and working on questions and it will get easier & easier Practice: Try to balance all the equations from the word & skeleton equations sheet Practice: Try to balance all the equations from the word & skeleton equations sheet