Balancing Equations D. Crowley, 2007

Balancing Equations To be able to balance equations To be able to balance equations

Symbols Remember, each element has its own symbol(s) - all found in the periodic table Remember, each element has its own symbol(s) - all found in the periodic table Every symbol begins with a capital, and may have one or more other non-capital letters which follow Every symbol begins with a capital, and may have one or more other non-capital letters which follow E.g. E.g. Oxygen = O Nitrogen = N Sodium = Na Magnesium = Mg Copper = Cu

Balancing A chemical reaction can be described by the process A chemical reaction can be described by the process reactants → products E.g. magnesium reacts with oxygen, producing magnesium oxide E.g. magnesium reacts with oxygen, producing magnesium oxide magnesium + oxygen → magnesium oxide 2Mg + O 2 → 2MgO

Balancing It is key you know how to balance the equations! It is key you know how to balance the equations! Remember: there must always be the same number of atoms on both sides Remember: there must always be the same number of atoms on both sides Numbers can only be put in front of the formula when it is needed Numbers can only be put in front of the formula when it is needed

Magnesium Oxide Look at the following reaction magnesium + oxygen → magnesium oxide 2Mg + O 2 → MgO You’ll notice, that there are more red and blue circles on the left hand side, than there are on the right You’ll notice, that there are more red and blue circles on the left hand side, than there are on the right To balance this, we can add a number in front of the right hand side To balance this, we can add a number in front of the right hand side 2Mg + O 2 → 2MgO

Water Look at the following reaction hydrogen + oxygen → water H 2 + O 2 → H 2 O Again there is a problem – this time we have an oxygen atom missing from the right hand side Again there is a problem – this time we have an oxygen atom missing from the right hand side To balance this, we can add a number in front of the right hand side To balance this, we can add a number in front of the right hand side H 2 + O 2 → 2H 2 O

Water But this is still unbalanced! hydrogen + oxygen → water H 2 + O 2 → 2H 2 O Finally, we can add a number in front of the hydrogen on the left hand side, to balance this up Finally, we can add a number in front of the hydrogen on the left hand side, to balance this up 2H 2 + O 2 → 2H 2 O

Example Look at the following reaction: Look at the following reaction: H 2 SO 4 + NaOH → Na 2 SO 4 + H 2 O The formulas are correct, but the number of atoms on the left are different from those on the right The formulas are correct, but the number of atoms on the left are different from those on the right Remember: we can only put numbers in front of the symbols… Remember: we can only put numbers in front of the symbols…

Balancing H 2 SO 4 + NaOH → Na 2 SO 4 + H 2 0 In the equation, there are more H atoms on the left, than there are on the right In the equation, there are more H atoms on the left, than there are on the right So we can add a 2 in front of the H 2 O on the right side So we can add a 2 in front of the H 2 O on the right side H 2 SO 4 + NaOH → Na 2 SO 4 + 2H 2 0 Now we have too many H and O atoms on the right hand side, so we can put a 2 in front of the NaOH on the left side Now we have too many H and O atoms on the right hand side, so we can put a 2 in front of the NaOH on the left side H 2 SO 4 + 2NaOH → Na 2 SO 4 + 2H 2 0 Now everything balances! Left hand side = 4 x H; 1 x S; 6 x O; 2 x Na Right hand side = 4 x H; 1 x S; 6 x O; 2 x Na

Questions Write a word equation for what happens when copper burns Write a word equation for what happens when copper burns How many reactants are there in this reaction? How many reactants are there in this reaction? What are these reactants? What are these reactants? What is the product of the reaction? What is the product of the reaction? When you find the mass at the end of the experiment, what chemical are you finding the mass of? When you find the mass at the end of the experiment, what chemical are you finding the mass of?Answers copper + oxygen → copper oxide copper + oxygen → copper oxide 2 Reactants 2 Reactants Reactants: copper + oxygen Reactants: copper + oxygen Product: copper oxide Product: copper oxide You are calculating the mass of the copper oxide You are calculating the mass of the copper oxide

Balance The Equations H 2 + O 2 → H 2 O H 2 + N 2 → NH 3 C 3 H 8 + O 2 → CO 2 + H 2 O Al + CuO → Al 2 O 3 + Cu K 2 O + H 2 O → KOH CaCl 2 + AgNO 3 → AgCl + Ca(NO 3 ) 2

Balance The Equations 2H 2 + O 2 → 2H 2 O 3H 2 + N 2 → 2NH 3 C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 O 2Al + 3CuO → Al 2 O 3 + 3Cu K 2 O + H 2 O → 2KOH CaCl 2 + 2AgNO 3 → 2AgCl + Ca(NO 3 ) 2