Balancing Chemical Reactions

Balancing Chemical Equations

Balancing Chemical Reactions Reactants: Zn + I 2 Product: Zn I 2

Balancing Equations: At the conclusion of our time together, you should be able to: 1.Review the various parts of a chemical equation and define each 2.Count the number of atoms on each side of an equation 3.Use conservation of matter to balance a chemical equation.

You Might Be a Hittite If… You come back from the dump with more than you took. You keep a can of Raid on the kitchen table.

A Balanced Equation A Balanced Equation Atoms can’t be created or destroyed Atoms can’t be created or destroyed Law of Conservation of Mass All the atoms we start with we must end up with 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). A balanced equation has the same number of each element on both sides of the equation (reactant and product sides).

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

Chemical Formula Counting up Atoms

NH 3 NH 3 _____ atoms of Nitrogen _____ atoms of Nitrogen _____ atoms of Hydrogen _____ atoms of Hydrogen _____ molecules/moles of NH 3 _____ molecules/moles of NH 3 NaCl NaCl _____ atoms of Sodium _____ atoms of Sodium _____ atoms of Chlorine _____ atoms of Chlorine _____ molecule/moles of NaCl _____ molecule/moles of NaCl Let’s Practice

8NaCl 8NaCl _____ atoms of Sodium _____ atoms of Sodium _____ atoms of Chlorine _____ atoms of Chlorine _____ molecule/moles of NaCl _____ molecule/moles of NaCl 3NH 3 3NH 3 ____ atoms of Nitrogen ____ atoms of Nitrogen ____ atoms of Hydrogen ____ atoms of Hydrogen ____ molecule/moles of NH 3 ____ molecule/moles of NH 3 Ca(NO 3 ) 2 Ca(NO 3 ) 2 _____ atoms of Calcium _____ atoms of Calcium _____ atoms of Nitrogen _____ atoms of Nitrogen _____ atoms of Oxygen _____ atoms of Oxygen _____ molecule/moles of Ca(NO 3 ) 2 _____ molecule/moles of Ca(NO 3 ) 2 8 Practice Again

More Practice SO 2 + 3H 2 O SO 2 + 3H 2 O _____ atoms of Sulfur _____ atoms of Sulfur _____ atoms of Hydrogen _____ atoms of Hydrogen _____ atoms of Oxygen _____ atoms of Oxygen _____ molecule/moles of SO 2 _____ molecule/moles of SO 2 _____ molecules of H 2 O _____ molecules of H 2 O

Let’s Step It Up a Little 2NH 4 NO 3 + 3H 2 S 2NH 4 NO 3 + 3H 2 S _____ atoms of Nitrogen _____ atoms of Nitrogen _____ atoms of Hydrogen _____ atoms of Hydrogen _____ atoms of Oxygen _____ atoms of Oxygen _____ atoms of Sulfur _____ atoms of Sulfur _____ molecule/moles of NH 4 NO 3 _____ molecule/moles of NH 4 NO 3 _____ molecule/moles of H 2 S _____ molecule/moles of H 2 S

You Must Be Joking! 2Na 2 CO 3 + 3CO 2 + 4NaCl + Mg(NO 3 ) 2 2Na 2 CO 3 + 3CO 2 + 4NaCl + Mg(NO 3 ) 2 _____ atoms of Sodium _____ atoms of Sodium _____ atoms of Carbon _____ atoms of Carbon _____ atoms of Oxygen _____ atoms of Oxygen _____ atoms of Chlorine _____ atoms of Chlorine _____ atoms of Nitrogen _____ atoms of Nitrogen _____ atoms of Magnesium _____ atoms of Magnesium _____ molecules/moles of Na 2 CO 3 _____ molecules/moles of Na 2 CO 3 _____ molecule/moles of CO 2 _____ molecule/moles of CO 2 _____ molecule/moles of NaCl _____ molecule/moles of NaCl _____ molecule/moles of Mg(NO 3 ) 2 _____ molecule/moles of Mg(NO 3 )

HITTITE INNOVATIONS:

C + O 2  CO 2 C + O 2  CO 2 This equation is already balanced This equation is already balanced What if it isn’t already? What if it isn’t already? C + O O  C O O

C + O 2  CO C + O 2  CO We need one more oxygen in the products. We need one more oxygen in the products. Can’t change the formula, because it describes what is produced. Can’t change the formula, because it describes what is produced. Remember, oxygen is a diatomic molecule. Remember, oxygen is a diatomic molecule. C + O  C O O

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

Must have started with two C’s Must have started with two C’s 2 C + O 2  2 CO 2 C + O 2  2 CO C + O  C O O O C C

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. Change a subscript to balance an equation. If you change the formula you are describing a different reaction. If you change the formula you are describing a different reaction. H 2 O is a different compound than H 2 O 2 H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not. 2 NaCl is okay, Na2Cl is not.

Another Hittite Innovation:

Example H 2 +H2OH2OO2O2  Make a table to keep track of where you are

Example H 2 +H2OH2OO2O2  Need twice as much O in the product RP H O

Example H 2 +H2OH2OO2O2  Changes the O RP H O

Example H 2 +H2OH2OO2O2  Also changes the H RP H O

Example H 2 +H2OH2OO2O2  Need twice as much H in the reactant RP H O

Example H 2 +H2OH2OO2O2  Recount RP H O

Example H 2 +H2OH2OO2O2  The equation is balanced, has the same number of each kind of atom on both sides RP H O

Example H 2 +H2OH2OO2O2  This is the answer RP H O Not this

7th Grade Science Answers "The body consists of three parts - the brainium, the borax and the abominable cavity. The brainium contains the brain, the borax contains the heart and lungs, and the abominable cavity contains the bowls, of which there are five - a, e, i, o, and u."

Subscripts vs. Coefficients The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound. The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

Balancing Equations: Let’s see if you can: 1.List the various parts of a chemical equation and define each 2.Count the number of atoms on each side of an equation

All You Really Need To Know You Can Learn From Noah's Ark 1. Don't miss the boat. 2. Don't forget that we're all in the same boat.

Chemical Equations 4 4 Al (s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) Black and Gray? Depict the kind of reactants and products and their relative amounts in a reaction. The blue numbers are called subscripts. The numbers in the front are called coefficients. The letters (s) and (g) are the physical states of compounds.

Balancing Chemical Reactions II

Balancing Equations

Balancing Equations: At the conclusion of our time together, you should be able to: 1.Use conservation of matter to balance a chemical equation.

Chemical Equations 4 Al(s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) This equation means 4 Al atoms + 3 O 2 molecules ---produces---> 2 molecules of Al 2 O 3 AND/OR 4 moles of Al + 3 moles of O 2 ---produces---> 2 moles of Al 2 O 3

Familiar Saying Freedom from guile or fraud constitutes the most excellent principle of procedure. Honesty is the best policy!

Ag + Cl 2 AgCl 1211 Both sides must be equal for ALL atoms.

Ag + Cl 2 AgCl 1211 Both sides must be equal for ALL atoms

Ag + Cl 2 AgCl 1211 Both sides must be equal for ALL atoms

CH 4 + O 2  CO 2 + H 2 O

Steps to Balancing Equations There are four basic steps to balancing a chemical equation. 1. Write the correct formula for the reactants and the products. DO NOT TRY TO BALANCE IT YET! You must write the correct formulas first. And most importantly, once you write them correctly DO NOT CHANGE THE FORMULAS! 2. Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side.

Steps to Balancing Equations 3. Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation. 4. Check your answer to see if: The numbers of atoms on both sides of the equation are now balanced. The numbers of atoms on both sides of the equation are now balanced. The coefficients are in the lowest possible whole number ratios. (reduced) The coefficients are in the lowest possible whole number ratios. (reduced)

Check Out This Actual Sign!!

Balancing Equations ___ H 2 (g) + ___ O 2 (g) ---> ___ H 2 O(l) 22 This equation is not balanced! Two hydrogen atoms from a hydrogen molecule (H 2 ) combines with one of the oxygen atoms from an oxygen molecule (O 2 ) to form H 2 O. Then, the remaining oxygen atom combines with two more hydrogen atoms (from another H 2 molecule) to make a second H 2 O molecule.

Balancing Equations ___ Al(s) + ___ Br 2 (l) ---> ___ AlBr 3 (s) 232

There is a Better Way to do This then just Trial-and-Error!! Some Suggestions to Help You: A. Look for singleton elements in compounds and determine the relationships. B. Do the hardest element to balance first keeping in mind the relationships from #1. C. Balance the lone elements last.

Balancing Equations Page 12:13 ____C 6 H 6 (g) + _____ O 2 (g) ----> _____CO 2 (g) + _____ H 2 O(g) ____B 4 H 10 (g) + _____ O 2 (g) ----> ___ B 2 O 3 (g) + _____ H 2 O(g) A 6A3A A 2A5A

Balancing Practice Problems Challenges Page 10:1 ____C 7 H 6 O 2 + _____ O > _____CO 2 (g) + _____ H 2 O(g) A 7A3A

Balancing Equations: Let’s see if you can: 1.Use conservation of matter to balance a chemical equation.

Balance Each of the Following Equations Page 11:6 ____Al 4 C 3 + _____ H 2 O ----> _____CH 4 + _____ Al(OH) 3 A 3A4A

Balance Each of the Following Equations Page 11:3 ____H 3 AsO > _____As 2 O 5 + _____ H 2 O 2A A3A 2 13

15 Helpful Hints On The Lab Report from Mr. T’s Vast Lab Experience!!! Hint #11. Given the most inappropriate time for something to go wrong, that's when it will occur.

Balancing Chemical Reactions from Words

Balancing Equations: At the conclusion of our time together, you should be able to: 1.Go from a word equation to a balanced chemical equation.

MAGIC NUMBERS 1. Take your house number and double it. 2. Add Multiply by Add your age. 5. Add the number of days in a non-leap year. 6. Subtract 615.

MAGIC NUMBERS What number do you have?? Look familiar???? _________________ - ________ Your house number Your age

Converting and Balancing Word Equations Sodium phosphate + iron (III) oxide  sodium oxide + iron (III) phosphate Na 3 PO 4 + Fe 2 O > Na 2 O + FePO

Converting Word Equations into Chemical Equations 14:8 Aluminum Oxide + Dihydrogen Monoxide  Aluminum hydroxide Al 2 O 3 + H 2 O ----> Al(OH) 3 3 2

Converting Word Equations into Chemical Equations 14:10 Strontium iodide + Lead (II) phosphate  Strontium phosphate + lead (II) iodide SrI 2 + Pb 3 (PO 4 ) > Sr 3 (PO 4 ) 2 + PbI 2 3 3

I Wouldn’t Throw That!!!