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Balancing Chemical Equations

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### Balancing Chemical Equations

### Balancing Chemical Equations subscript of the element to count the atoms. Then list the number of atoms of each element on each side.

What goes in must come out!

Balancing Chemical Equations

- Balancing a chemical equation is much like the work of an accountant who has to show every penny that comes in and where it has gone to.
- Or your parents balancing the family budget.

Objectives

- Learn the steps to balancing chemical equations.
- Take notes to help you understand.
- Test yourself with a set of equations to balance.
- Enter your own equations to see if they balance.

Essential Question

- What do the “Conservation Laws” tell us?

Law of Conservation of MassYou need to remember this law!

- The Law of Conservation of Mass states: that mass is neither created nor destroyed in any chemical reaction. Therefore balancing of equations requires the same number of atoms on both sides of a chemical reaction.
- The number of atoms in the Reactants must equal the Number of atoms in the Products

Chemical Equations

Because of the principle of the Conservation of Matter,

an equation must be balanced.

It must have the same number of atoms of the same kind on both sides.

Law of Conservation of Mass

- The mass of all the reactants (the substances going into a reaction) must equal the mass of the products (the substances produced by the reaction).
- Reactant + Reactant = Product

A simple equation, such as the synthesis of Iron (II) sulfide,

- iron + sulfur Iron (II) sulfide
- Fe + S FeS
- Note that in a chemical equation, by convention, we use the arrow “ " instead of the equals “ = ".

- The last stage is to put in state of matter symbols, (s, l, g, aq), as appropriate (solid, liquid, gas, aqueous or dissolved in water)
- Fe(s) + S(s) FeS(s)

Balancing g, aq), as appropriate (solid, liquid, gas, aqueous or dissolved in water) Equations

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

2

3

Write all reactants on the left and all products on the right side of the equation arrow. Make sure you write the correct formula for each element

2. Use coefficients in front of each formula to balance the number of atoms on each side.

Steps to Balancing a Chemical Equation3. Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list the number of atoms of each element on each side.

4. It is often easiest to start balancing with an element that appears only once on each side of the arrow. These elements must have the same coefficient. Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.

Steps to Balancing a Chemical EquationRe-cap of steps from rule 4: subscript of the element to count the atoms. Then list the number of atoms of each element on each side.

- Balance elements that appear only once on each side of the arrow.
- Next balance elements that appear only once on each side but have different numbers of atoms.
- Finally balance elements that are in two formulas in the same side.

An easier way

Then all you do is list the atoms that are involved on each side of the arrow

Mg + O2 MgO

First you need an equation with the correct “formulae” ………. You’ll probably be given this in the question

Just like this one

Mg + O2 MgO

M O

M O

Mg + O side of the arrow2 MgO

Mg + O2 MgO

Mg

O

Mg

O

1

1

2

1

Then start balancing:

[1] Just count up the atoms on each side

1

1

2

1

[2] The numbers aren’t balanced so then add “BIG” numbers to make up for any shortages

2

2

2

And adjust totals

2 side of the arrow

2

1

Mg + O2 MgO

2

2

Mg

O

But the numbers still aren’t equal, so add another “BIG” number

2

2

And adjust totals again

NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS

WE SAY THAT THE EQUATION IS BALANCED!!

Try to balance these equations using the same method: side of the arrow

[1] Na + Cl2 NaCl

[2] CH4 + O2 CO2 + H2O

[3] Li + HNO3 LiNO3 + H2

[4] Al + O2 Al2O3

How did you get on?? side of the arrow

Here are the answers:

[1] 2 Na + Cl22 NaCl

[2] CH4 + 2 O2 CO2 + 2 H2O

[3] 2 Li + 2 HNO3 2 LiNO3 + H2

[4] 4 Al + 3 O22 Al2O3

HOPE YOU’VE GOT THE IDEA… REMEMBER TO CHECK THAT YOU CAN DO ELECTROLYSIS EQUATIONS TOO

Example side of the arrow

- NH3 + O2 NO + H2O
ReactantsProducts

- N appears once on both sides in equal numbers, so the coefficient for NH3 is the same as for NO.

Example: side of the arrowNH3 + O2 NO + H2O

- Next look at H which appears only once on each side but has different numbers of atoms, 3 on the left and 2 on the right. The least common multiple of 3 and 2 is 6, so rewrite the equation to get 6 atoms of H on both sides:
- 2NH3 + O2 NO + 3H2O

Example: side of the arrow2NH3 + O2 NO + 3H2O

- There are 2 oxygen atoms on the left and 5 on the right — the least common multiple of 2 and 5 is 10, so rewrite the equation as:
- 2NH3 + 5O24NO + 6H2O

Now count the atoms on each side: side of the arrow

- 2NH3 + 5O2 4NO + 6H2O
- Write them out keeping them on the appropriate side of the chemical equation
- 2 N (nitrogen atoms)4 N (nitrogen atoms)
- 6 H (hydrogen atoms) 12 H (hydrogen atoms)
- 10 O (oxygen atoms)10 O (oxygen atoms)
- This shows the equation not to be balanced “YET”

Check the number again: side of the arrow

- If you double the N and H on the left the equation will be balanced:
- 4NH3 + 5O2 4NO + 6H2O

Double-check: side of the arrow

- 4NH3 + 5O2 4NO + 6H2O
- 4 N (nitrogen atoms)4 N (nitrogen atoms)
- 12 H (hydrogen atoms)12 H (hydrogen atoms)
- 10 O (oxygen atoms)10 O (oxygen atoms)
- The equation is Balanced

Balancing Practice side of the arrow

- For more help go to: http://richardbowles.tripod.com/chemistry/balance.htm#part0
- For some fun balancing equations go to:
- http://www.mpcfaculty.net/mark_bishop/balancing_equations_tutorial.htm

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