Chemical Reactions and Chemical Reactions and Balancing EquationsBalancing Equations

March 27, 2013March 27, 2013

ObjectivesObjectives

1.1. Explain the difference between elemental Explain the difference between elemental and chemical formulaand chemical formula

2.2. Recognize all the parts of a chemical Recognize all the parts of a chemical equationequation

3. Explain what is meant by a balanced chemical equation

4. Demonstrate how to write simple balanced chemical equations

Chemical BondingChemical Bonding

Chemical changes occur because of Chemical changes occur because of breaking and rearrangement of chemical breaking and rearrangement of chemical bonds:bonds: The attraction between two atoms that holds The attraction between two atoms that holds

them togetherthem together

Chemical change = chemical reactionChemical change = chemical reaction

Chemical EquationChemical Equation

To show chemical reactions we use To show chemical reactions we use chemical equationschemical equations

C + OC + O22 CO CO22

44 Al Al (s)(s) + + 33 OO2 (g)2 (g) ---> ---> 22 AlAl22OO3 (s)3 (s)

Parts of Chemical EquationParts of Chemical Equation

Elemental formula:Elemental formula: how atoms are how atoms are bounded together in an elementbounded together in an element LiLi OO22 , N , N22 , S , S88

Chemical formula:Chemical formula: representation representation of a compound, when atoms of of a compound, when atoms of different elements bond to each otherdifferent elements bond to each other NaCl, NHNaCl, NH3 3 , CO, CO22

Coefficient:Coefficient: represents how represents how many of a many of a particular element particular element or moleculeor molecule

Subscript:Subscript: represents how represents how many of a many of a particular atomparticular atom

How many atoms?How many atoms?

C + OC + O22 CO CO22

44 Al Al (s)(s) + + 33 OO2 (g)2 (g) ---> ---> 22 AlAl22OO3 (s)3 (s)

(s) represents solid

(l) represents liquid

(g) represents gas

(aq) represents aqueous

Chemical EquationChemical Equation

Reactants Reactants Products Products

C + OC + O22 CO CO22

when reading an equation Arrow = yieldswhen reading an equation Arrow = yields

Agenda Bell Work

• Finish balancing notes

• Practice

• Ionic Puzzle Piece activity

• Review for quiz

Law of Conservation of Mass

Matter is neither created nor destroyed during a chemical reaction

Therefore all chemical equations must be balanced; equal atoms of each element on each side

Balancing equation rules

You may change the coefficients in front

You may NOT change the subscripts

Changing the subscript changes the compound

Steps of balancing

1. Write the correct formulas for the equation. Once written do not change the formula’s

2. Find the number of atoms on the left side of each element and compare it against the number of atoms of the same elements on the right side

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 coefficients are in the lowest possible whole number ratios. (reduced)

Helpful hints

Take one element at a time working left to right,

Leave H for next to last and O last

IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again.

Balancing Equations___ H2(g) + ___ O2(g) ---> ___ H2O(l)

One of the oxygen atoms

binds with two of the

hydrogen atoms

Done ActivitiesWhich equations are balanced?

Balance the ones that aren’t

a.Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

b. 3Al(s) + 3Br2(l) Al2Br3(s)

c. 2HgO(s) 2Hg(l) + O2(g)

___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

____C3H8(g) + _____ O2(g) ---->

_____CO2(g) + _____ H2O(g)

____B4H10(g) + _____ O2(g) ---->

_____B2O3(g) + _____ H2O(g)