1 of 13

Generating & Balancing Equations

Course: SCH4C

2 of 13

Recall:

“The Law” of Conservation of Mass

“The law stating that during a chemical reaction matter is neither created nor destroyed.”

3 of 13

Learning Goals

01.

02.

03.

Interpret reactions as described by a chemical equation

Determine the number of atoms in a molecular formula

Analyze chemical reactions and balance the number of atoms involved

Today, learners will:

4 of 13

But first…

Find your periodic table!

What is the only letter in the alphabet that does not appear on the periodic

table of elements?

5 of 13

  1. REVIEW: Interpreting Chemical Equations

1C + 2H2 → 1CH4

​

​

Element

Symbol

Subscript indicates the Number of Atoms and/or state

Coefficient indicates the Number of Molecules

Direction of Reaction

REACTANTS PRODUCTS

6 of 13

C + H H →

H H

Element

Number of Atoms Reacting

Number of Atoms Produced

C

1

1

H

4

4

C + 2H2 → CH4

7 of 13

2. Time to Count!

Remember: There are different ways to represent a molecular formula!

2

H -- H Cl -- Cl 2 x H -- Cl

H2 + Cl2 = 2 HCl

8 of 13

What do you notice about this

chemical equation?

O = 3, N = 1, H = 2

O = 4, N = 2, H = 1

9 of 13

Given the molecular formulae, determine the number of atoms present in the following balanced chemical reaction.

Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq)

Why are nitrogen (N) and oxygen

(O) grouped as an element for the

purpose of counting atoms?

Element

Number of Atoms Reacting

Number of Atoms Produced

Cu

1

1

Ag

2

2

NO3-

2

2

How do we know

the equation is

balanced?

10 of 13

Comedic Break

Why can you never trust an atom?

11 of 13

3. Balancing Chemical Reactions

The Inspection Method

  • Compare the number of atoms of each element on the products side and the reactants side
  • Multiply, or divide when appropriate, the coefficients (number of molecules) accordingly to balance the equation
  • This method involves trial and error, but is more simplistic than the Algebraic Method which uses linear equations

​

12 of 13

Rules & Helpful Hints

  • ONLY coefficients can be modified to balance the equation
    • Subscripts canNOT be modified, as this would change the molecules and reaction
    • Balance polyatomic ions as a group
    • Diatomic elements: H O F Br I N Cl
  • Tip: Start with singular atoms and balance Oxygens and Hydrogens at the end
  • Recall: No coefficient = 1 molecule
  • CHECK YOUR ANSWER!
    • Does the equation follow the Law of Conservation of Mass?

13 of 13

Sample Problem

Write a balanced equation for the reaction between solid sodium and water to produce aqueous sodium hydroxide precipitate and hydrogen gas.

2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + __ H2

Reactants

Na = 2

H = 4

O = 2

​

Products

Na = 2

H = 4

O = 2

​