2 If a chemical equation does not obey the law of conservation of mass the equation is said to be what?NOT BALANCEDSo Let’s look at the steps we need to take toBALANCE chemical equationsLet’s work with the following equation:Fe O2 Fe2O3
3 Step 1. Create a RAP table(what’s a RAP table ??)A table that shows us what atoms are present in thisreaction, how many there are and are they reactantsor products?For example:Fe O2 Fe2O3#R atom #PFeO
4 Rule 2. Go to the first atom that’s not balanced and balance it! Since Fe atoms are not balanced what do we need to do to balance it?Right! Multiply it by 2 (Only multiply)#R atom #P1 Fe 22 O 32x
5 In step 2 we balanced the number of Fe atoms by multiplying the reactant side by 2. This now becomes the new coefficient in the chemical equation.Modify the equation to reflect the change#R atom #P1 Fe 22 O 32Fe O2 Fe2O32xAre all atoms balanced?
6 3. Move to the next unbalanced atom. What is it? #R atom #PFeOHow can we balance theOxygen?Multiply Reactants by 3 and Products by 2Adjust the equation to reflect yourchanges#R atom #PFe3x O x22Fe O2 2Fe2O3But notice that by changing Oxygen we alsoChanged Iron. We need to go back and fix this.
7 4. Write out the updated RAP table. How can we Balance the Iron?#R atom #PFeOSure! Multiply the # ofReactant Fe atoms by 2 !2xRe-write the equation reflectingThe new changes you’ve made.4Fe O2 2Fe2O3Do we have a balanced Chemical Equation now?Yes we do!
8 Polyatomics #R atom #P 2 Ag 2 2 NO3 2 Mg 1 2 Cl 2 When an equation has Polyatomics in it, such as in thisBalanced chemical equation2AgNO3 + MgCl2 2AgCl + Mg(NO3)2And the polyatomic appears on BOTH the reactant and productSide of the equation Count the polyatomic as an “ATOM”So the above reactant atoms would be:#R atom #PAgNO3 2Mg 12 Cl 2If the same polyatomic does notAppear on both sides break thePolyatomic down into atoms!
10 Is this equation balanced? NaOH + CaBr2 Ca(OH)2 + NaBrWhat atoms do we have inThis equation?Count atoms & Startthe RAP table#R atom #PNAOHCaBr2) Do the #Reactant atoms = the # of Product atoms?3) So pick the 1st unbalanced atom & begin balancing
11 We’ll start with balancing Hydroxide NaOH + CaBr2 Ca(OH)2 +NaBrHow can we make both Hydroxides equal?#R atom #PNaOH 2CaBrSure we’ll multiply #R OH by 2Next step> rewrite the modified eqn.2x2NaOH + CaBr2 Ca(OH)2 + NaBrHydroxide is now balanced so let’s move to the nextUnbalanced atom, which is? …
12 What can we do to balance the Bromine? Sure! Multiply the #P Bromine by 2Now adjust the table to reflectThe changes and then rewrite theEqn.#R atom #PNa 1OH 2CaBr 1x22NaOH + CaBr2 Ca(OH)2 + 2NaBr
13 Let’s update the RAP table with the new #’s Based on our updated equation.2NaOH + CaBr2 Ca(OH)2 + 2NaBr#R atom #P2 NaOHCaBrAre we now balanced?Sure!
14 Ok Try Balancing this equation: C2H6 + O2 CO2 + H2O#R atom #PCHOStep 1. Total up the atomsStep 2. Balance the #P Carbon#R atom #PCHO& Re-write the equationC2H6 + O2 2CO2 + H2OAre we done?
15 Step 3. Carbons are balanced now but Hydrogen isn’t. So, balance Hydrogen atoms next#R atom #PCHOMultiply #P Hydrogen by 3x3Step 4. Re-write the eqn. &Retotal the number of atomsC2H6 + O2 2CO H2O#R atom #PCHOCarbon and Hydrogen are nowbalanced but oxygen isn’t.
16 Step 5. To balance Oxygen multiply O by 3½ #R atom #PCHOStep 6. Re-write the eqn. &Retotal the numberof atoms3 ½ xC2H ½ O2 2CO H2OIt looks like we’re balanced. But, are we?No! We can’t have 3 ½ Oxygen molecules! Only wholeNumbers are allowed.So what do we need to do to fix this?
17 Step 7. Let’s clean this up by Multiply everything by 2 C2H ½ O2 2CO H2Ox 22C2H O2 4CO H2O#R atom #PCHOStep 8. Retotal #R and the#P atomsAre we balanced?YES!
18 Try this problem NH4OH + FeCl3 Fe(OH)3 + NH4Cl Start here. Recognize weHave polyatomics but theyAppear on both sides of theEquation.#R atom #PNH4 1OH 3FeClOK … Now finish it up
19 Answer to previous problem 3NH4OH + FeCl3 Fe(OH)3 + 3NH4Cl