Review from yesterday’s lesson  We are learning how to balance equations because the conservation of mass says that the mass before a reaction must be the same as the mass after a reaction. Atoms cannot be created nor destroyed H 2 + O 2 ---> H 2 O

Review from yesterday’s lesson  We must know how to count the number of atoms in a substance before we can balance  6Na 2 O 3  Coefficient = 6  Subscript Na= 2  Subscript O= 3  Total number of Na= 6 X 2= 12  Total number of O= 6 X 3= 18

Is the blue number a coefficient or a subscript? Na 2 CO 3 4K 2 PO 4 6H 2 0 3Li 2H 3 PO 4 2Mg(OH) 2 6LiCl 4

Count the number of atoms 5H 2 CO 3 How many H atoms? 5 X 2= 10 How many C atoms? 5 X 1= 5 5 X 1= 5 How many O atoms 5 x 3= 15 5 x 3= 15 Click here to go to balancing equations steps

Balancing Equations Are you up for the challenge?

Why do you need to balance equations?  Let’s read page  The Law of Conservation of Mass says that the mass of the reactants must equal the mass of the products.  In this example: H 2 + O 2 ---> H 2 O There are 2 hydrogen’s on the left and 2 Oxygen’s, but there is only 1 oxygen on the right.

H 2 + O 2 ---> H 2 O  The reactants do not equal the products!  Where did the extra oxygen go?  Atoms can’t be created nor destroyed.  They didn’t go anywhere, you just need to add numbers so the sides become equal  An equation is balanced by changing coefficients in a somewhat trial-and-error fashion

Important Vocabulary- Coefficient  Coefficient- Large number located in front of an element or compound in a chemical formula. 2H= 2 hydrogen's  4H 2 0  Coefficient is 4  H 2 O H 2 O H 2 O H 2 O

Important Vocabulary- Subscript  Subscript- The small number that is in the lower right corner of an element H20H20H20H20  Subscript is 2  2 hydroden’s H H

 If there is no coefficient or subscript- assume it is 1 C S 2  Coefficient=1  C’s subscript= 1  S’s subscript= 2 1 1

Let’s practice  Na O  H PO  H O  S  K

Math Review  Distributive Property- The coefficient times the subscript gives the total number of atoms. 4H 2 0  H= 4 X 2= 8 Hydrogen’s  O= 4 X 1= 4 Oxygen’s 1

Math Review 4Mg(OH) 2  Mg= 4 X 1= 4  OH= 4 x 2= 8 1

3KOH  How many K atoms do I have? Coefficient 3 Subscript 1 3 X1= 3  How many O atoms do I have? Coefficient 3 Subscript 1 3 X 1= 3  How many H atoms do I have? Coefficient 3 Subscript 1 3 X 1= 3

3K 2 O  How many K atoms do I have?  Coefficient 3  Subscript 2  3 X 2= 6  How many O atoms do I have?  Coefficient 3  Subscript 1  3 X 1= 3

2H 2 O  How many H atoms do I have?  Coefficient= 2  Subscript= 2  2 X 2= 4  How many O atoms do I have?  Coefficient= 2  Subscript= 1  2 X 1= 2

K 3 PO 4  How many K atoms do I have?  Coefficient= 1  Subscript= 3  1 X 3= 3  How many P atoms do I have?  Coefficient= 1  Subscript= 1  1 X 1= 1  How many O atoms do I have?  Coefficient= 1  Subscript= 4  1 X 4= 4

Mg 3 (PO 4 ) 2  How many Mg atoms do I have?  Coefficient= 1  Subscript= 3  1 X 3= 3  How many P atoms do I have?  Coefficient= 1  Subscript=1 X 2= 2  1 X 2= 2  How many O atoms do I have?  Coefficient= 1  Subscript= 4 X 2=8  1 X 8= 8

Steps for balancing equations  1. Draw boxes around all the chemical formulas.  Never, ever, change anything inside the boxes. Ever. Really. If you do, you're guaranteed to get the answer wrong. H 2 + O 2 ---> H 2 O

Steps for balancing equations  2. Make an element inventory.  How are you going to know if the equation is balanced if you don't actually make a list of how many of each atom you have? You won't. You have to make an inventory of how many atoms of each element you have, and then you have to keep it current throughout the whole problem.  See example on next slide

H 2 + O 2 ---> H 2 O ReactantsProducts Hydrogen (H) 22 Oxygen (O) 21

But what if you have more than one formula on each side of the equation? Let’s practice with the REACTANTS!  NaOH + H 2 CO 3 Na 2 CO 3 + H 2 O How many Na atoms do I have? 1 X 1 =1 How many O atoms do I have? 1 X 1= 11 X 3= = 4 How many H atoms do I have? 1 X 1= 11 X 2= = 3 How many C atoms do I have? 1 X 1= 1

Steps for balancing equations  3. Write numbers in front of each of the boxes until the inventory for each element is the same both before and after the reaction.  Whenever you change a number, make sure to update the inventory - otherwise, you run the risk of balancing it incorrectly. When all the numbers in the inventory balance, then the equation can balance,

H 2 + O 2 ---> H 2 O H 2 + O 2 ---> H 2 O ReactantsProducts Hydrogen (H) 22 Oxygen (O) Notice- I put the coefficient in front of the box- NOT inside!

Steps for balancing equations  4. Find the elements which appear in the fewest numbers of molecules and balance these first.  Continue in sequence until you balance the element which appears in the most molecules last.  Tip: Start by balancing an element that appears in only one reactant and product.

H O H 2 + O 2 H 2 O Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP

Rules  You cannot change a subscript.  You cannot place a coefficient in the middle of a formula. H 2 + O 2 ---> H 2 2O  Make sure that your final set of coefficients are all whole numbers with no common factors other than one.  For example, this equation is balanced:  4 H O 2 ---> 4 H 2 O  However, all the coefficients have the common factor of two. Divide through to eliminate common factors like this.

If you run into problems trying to figure out the answer…  Sometimes, you will need to find the lowest common multiple in order to make an inventory balance! H22 O27 RP The lowest common multiple between 2 and 7 is 14 14

If you run into problems trying to figure out the answer…  What happens when the only way you can get a problem to work out is to make one of the numbers a decimal or fraction?  When this happens, find the largest molecule in the equation and stick a "2" in front of it.  Then start the problem over.  Will this work all the time? Well, no. But it will work sometimes, and give you a new strategy for hard problems.

C S C + S 8 CS Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP How do I get the S’s in the products to equal 8?

Na O Na + O 2 Na 2 O Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP

N O N 2 + O 2 N 2 O Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP 5 10 HINT: Find the lowest common multiple of the Oxygen molecules

Na O Na + O 2 Na 2 O Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP How do I get the Na’s in the reactants to equal 2?

K + B 2 O 3 K 2 O + B 2 6 Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! 3 ReactantsProducts K B O HINT: Start on the products side- and start with the element with the lowest number of molecules

N H N 2 + H 2 NH Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP

Cs N Cs + N 2 Cs 3 N Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP

` Li + AlCl 3 LiCl + Al 3 3 Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP Li Al Cl

NaOH + H 2 CO 3 Na 2 CO 3 + H 2 O 2 2 Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! Hint: We are going to start with the Na on the reactant side because it is not balanced and has the lowest number of molecules RP Na O H C

C 2 H 6 + O 2 CO 2 + H 2 O 6 2 Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP C H O Hint: We are going to look for the common factor of H’s

H 3 PO 4 + KOH K 3 PO 4 + H 2 O 3 3 Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP H P O K Hint: We are going to look for the lowest number of molecules that are not balanced.

Na + NaNO 3 Na 2 O + N Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP Na N O Hint: We are going to look for the next common factor of 1 and 3

H 3 PO 4 + Mg(OH) 2 Mg 3 (PO 4 ) 2 + H 2 O H 3 PO 4 + Mg(OH) 2 Mg 3 (PO 4 ) 2 + H 2 O 3 2 Step 1: Write formula and draw boxes Step 2: Make an element inventory Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go! RP H P O Mg