Balancing Chemical Equations ppt

3.  Chemical equation - Describes a chemical change.
 Parts of an equation:
2Ag + H2S Ag2S + H2
Reactant Product
Reaction symbol

4.  Reactant - The chemical(s) you start with before the
reaction.
 Written on left side of equation.
 Product - The new chemical(s) formed by the
reaction.
 Right side of equation.

5.  Subscript - shows how many atoms of an element are
in a molecule.
 EX: H2O
 2 atoms of hydrogen (H)
 1 atom of oxygen (O)
 Coefficient - shows how many molecules there are of
a particular chemical.
 EX: 3 H2O
 Means there are 3 water molecules.

6. 1) 2CrCl3
2) Ba(OH)2 3) 3Ca(ClO3)2
Counting Atoms - Multiply coefficient by
subscript of each element.
• If in parenthesis, the subscript after the
parenthesis is multiplied to the chunk of
everything in the parenthesis than multiplied
by coefficient.
Cr – (2x1) = 2
Cl – (2 x 3) = 6
Ba – 1
O – (2x1) = 2
H – (2 x 1) = 2
Ca – (3x1) = 3
Cl – (2 x 3) = 6
O – (3 x 3 x 2) = 18

7.  2H2 + O2  2H2O

8.  In a chem. rxn, matter is neither created nor
destroyed.
 In other words, the number and type of atoms going
INTO a rxn must be the same as the number and type of
atoms coming OUT.
 If an equation obeys the Law of Conservation, it is
balanced.

9.  CH4 + O2  CO2 + H2O
Reactant Side Product Side
1 carbon atom
4 hydrogen atoms
2 oxygen atoms
1 carbon atom
2 hydrogen atoms
3 oxygen atoms

10. A Balanced Equation
 CH4 + 2O2  CO2 + 2H2O
Reactant Side Product Side
1 carbon atom
4 hydrogen atoms
4 oxygen atoms
1 carbon atom
4 hydrogen atoms
4 oxygen atoms

11. 1. Matter cannot be created or destroyed.
2. Subscripts cannot be added, removed, or changed.
3. You can only change coefficients.
4. Coefficients can only go in front of chem.
formulas...NEVER in the middle of a formula.
A few extra tips:
Try balancing big formulas first; save free elements for last.
If the same polyatomic ion appears on both sides of the
equation, it’s usually okay to treat it as one unit.
There is no one particular way to balance equations. Some
equations are harder to balance than others and might require
some creativity to solve.

12. 1) Determine the number of atoms for each element.
2) Pick an element that is not equal on both sides of
the equation.
3) Add a coefficient in front of the formula with that
element and adjust your counts.
4) Continue adding coefficients to get the same
number of atoms of each element on both sides

13. 1. Every atom in _________becomes part of the
___________.
2. Atoms are never ___________ or _________
3. Scientists know that there must be the ________
number and type of atoms on each ________ of the
equation.
3. Balance by using ____________ in front of the
chemical formulas because you can not add or change
___________of a correct formula
reactants
products
created destroyed
coefficients
subscripts
same
side

14. Step 1: Determine the number of atoms for each
element.
Mg + O2 MgO
Mg = 1 Mg = 1
O = 2 O = 1

15. Step 2: Pick an element that is not equal on both sides
of the equation.
Mg + O2 MgO
Mg = 1 Mg = 1
O = 2 O = 1 Since the O atoms
are not equal, we’ll
target those first.

16. Step 3: Add a coefficient in front of the formula with the
element and adjust your counts.
Mg + O2 2 MgO
Mg = 1 Mg = 1 2
O = 2 O = 1 2 Adding a 2 in front
of MgO will change
the number of atoms
on the product side
of the equation.

17. Step 4: Continue adding coefficients to get the same
number of atoms of each element on each
side.
2 Mg + O2 2 MgO
Mg = 1 2 Mg = 1 2
O = 2 O = 1 2
Now we need to increase the number of Mg atoms we have on the
reactants side. Adding a coefficient 2 in front of Mg will give us 2
atoms of Mg and balance the equation.

18.  Balance the following equation by adjusting
coefficients.
reactants products
N
H
N2 + H2  NH3
2
2
1
3
2
2
6
3
6

19.  Balance the following equation by adjusting
coefficients.
KClO3  KCl + O2
reactants products
K
Cl
O
1
1
1
1
3 2
3
2
2
2
6 6
2
2
2

20.  Balance the following equation:
 Fe + O2  Fe2O3
2
3
4

21.  Balance the following equation:
 C2H6 + O2  CO2 + H2O
4 6
7
2

22. How can a balanced chemical equation be interpreted?

23.  Change in color
 Formation of a solid (a precipitate)
 Evolution of gas (bubble formation)
 Change in temperature (heat is released or
absorbed)

24. Decomposition reaction – a reactant
breaks down into two or more products

25. Synthesis / Combination reaction –
two or more reactants form a single product

26. Single displacement reaction – one
element replaces another in a compound

28. Double displacement reaction – two
ionic compounds exchange ions

29. Combustion reaction – a hydrocarbon (a
compound containing carbon and hydrogen) reacts
with oxygen to form carbon dioxide and water.