CHEMISTRYCHEMISTRY

November 7November 7thth, 2011, 2011

Warm Up Warm Up What is wrong with the following What is wrong with the following

equation?? Can you equation?? Can you fixfix it? it? HINT: think Law of Conservation of MassHINT: think Law of Conservation of Mass

HH22 + O + O22 H H22OO

CHEMISTRY LAUGHSCHEMISTRY LAUGHSWhy does hamburger have lower energy Why does hamburger have lower energy

than steak?than steak?

AgendaAgenda

Unit 7: Balancing EquationUnit 7: Balancing Equation PracticePractice

Balancing EquationBalancing Equation

Word EquationsWord Equations Describes a chemical reaction that Describes a chemical reaction that

occurs using the occurs using the namesnames of the of the chemicals involved.chemicals involved.

ReactantsReactants versus versus ProductsProducts An arrow is written between the An arrow is written between the

reactants and products to indicate that reactants and products to indicate that chemical chemical changechange is occurring is occurring– For example: 2HFor example: 2H22 + O + O22 2H 2H22OO

Balancing EquationBalancing Equation

Atoms involved in a chemical reaction Atoms involved in a chemical reaction must be must be balancedbalanced..– SameSame number of atoms of each number of atoms of each elementelement on on

both sides of a chemical equation.both sides of a chemical equation. Unbalanced equationUnbalanced equation

– Balance the equation by adding coefficients Balance the equation by adding coefficients in in frontfront of the compounds of the compounds CoefficientsCoefficients: number of molecules of a particular : number of molecules of a particular

compoundcompound SubscriptsSubscripts: number of atoms of each element in : number of atoms of each element in

the compoundthe compound

Balancing EquationsBalancing EquationsA.A. From the word equation, write the From the word equation, write the correctcorrect

formula for all reactants and products.formula for all reactants and products.B.B. If given an unbalanced equations first, balance If given an unbalanced equations first, balance

the equation by using coefficients:the equation by using coefficients:1.1. NEVER change the NEVER change the subscriptssubscripts in the formula to in the formula to

balance the equationbalance the equation2.2. Elements need to be balanced from Elements need to be balanced from eithereither side of side of

the equationthe equation3.3. Start with the Start with the firstfirst element and work right of the element and work right of the

equationequation4.4. Balance the number of oxygen and hydrogen atoms Balance the number of oxygen and hydrogen atoms

afterafter all the other elements have been balanced. all the other elements have been balanced.C.C. Go back and double check that all elements Go back and double check that all elements

are balancedare balancedD.D. BOX your coefficients when finishedBOX your coefficients when finishedE.E. USE PENCIL only! (you will be erasing A LOT!)USE PENCIL only! (you will be erasing A LOT!)

Balancing EquationBalancing Equation

Inspection MethodInspection Method Algebraic MethodAlgebraic Method

Practice and ReasoningPractice and Reasoning

Unbalanced Equation:Unbalanced Equation:– SnOSnO22 + H + H22 → Sn + H → Sn + H22OO

Look at the equation and see which Look at the equation and see which elements are not balanced. In this elements are not balanced. In this case, there are two oxygen atoms on case, there are two oxygen atoms on the left-hand side of the equation and the left-hand side of the equation and only one on the right-hand side. only one on the right-hand side. Correct this by putting a coefficient of Correct this by putting a coefficient of 2 in front of water.2 in front of water.– SnOSnO22 + H + H22 → Sn + 2 H → Sn + 2 H22OO

– SnOSnO22 + H + H22 → Sn + 2 H → Sn + 2 H22OO This puts the hydrogen atoms out of This puts the hydrogen atoms out of

balance. Now there are two hydrogen balance. Now there are two hydrogen atoms on the left and four hydrogen atoms atoms on the left and four hydrogen atoms on the right. To get four hydrogen atoms on the right. To get four hydrogen atoms on the right, add a coefficient of 2 for the on the right, add a coefficient of 2 for the hydrogen gas. Remember, coefficients are hydrogen gas. Remember, coefficients are multipliers, so if we write 2 H2O it denotes multipliers, so if we write 2 H2O it denotes 2x2=4 hydrogen atoms and 2x1=2 2x2=4 hydrogen atoms and 2x1=2 oxygen atoms.oxygen atoms.– SnOSnO22 + 2 H + 2 H22 → Sn + 2 H → Sn + 2 H22OO

The equation is now balanced. Be sure to The equation is now balanced. Be sure to double-check your math! Each side of the double-check your math! Each side of the equation has 1 atom of Sn, 2 atoms of O, equation has 1 atom of Sn, 2 atoms of O, and 4 atoms of H.and 4 atoms of H.

Practice ProblemsPractice Problems

__Fe + __Cl__Fe + __Cl22 __FeCl __FeCl33

__Cr + __O__Cr + __O22 __Cr __Cr22OO33

__Na + __H__Na + __H22O O __NaOH + __H __NaOH + __H22

__Ca(CN)__Ca(CN)22 + __AlF + __AlF33 __CaF __CaF22 + __Al(CN) + __Al(CN)33

Word ProblemWord Problem Potassium phosphate + Calcium hydroxide Potassium phosphate + Calcium hydroxide

Calcium phosphate + Potassium hydroxideCalcium phosphate + Potassium hydroxide

__K__K33(PO(PO44) + __Ca(OH)) + __Ca(OH)22 __Ca __Ca33(PO(PO44))22 + __KOH + __KOH

2K2K33(PO(PO44) + 3Ca(OH)) + 3Ca(OH)22 __Ca __Ca33(PO(PO44))22 + 6KOH + 6KOH ReactantsReactants ProductsProducts

K = 6K = 6 K = 6K = 6P = 2P = 2 P = 2P = 2Ca = 3Ca = 3 Ca = 3Ca = 3O = 14O = 14 O = 14O = 14H = 6H = 6 H= 6H= 6

HomeworkHomework

Unit 7 Balancing Equation Worksheet Unit 7 Balancing Equation Worksheet 11