Balancing Chemical Equations

​Balancing Chemical Equations

By Victor Castillo

Balancing Chemical Equations

Multiple Choice

What does the Law of Conservation of Mass say? It says,

"During a chemical reaction, mass is neither _______ or destroyed."

• burned

• created

• melted

Multiple Choice

The substances that go into a reaction are called the _______.

• products

• reactants

Multiple Choice

So, the Law of Conservation of Mass would tell us that the mass of all the REACTANTS must __________ the mass of all PRODUCTS in a chemical reaction.

• equal

• be greater than

• be less than

Multiple Choice

An ENDOTHERMIC reaction would feel ______ to the touch, while an EXOTHERMIC reaction would feel ______ to the touch.

• hot ; cold

• cold ; hot

2H₂ + O₂ ---> 2H₂O

This equation is BALANCED on both sides.

Notice that there are 4 Hydrogens and 2 Oxygens on each side.

The full-size numbers to the LEFT of the elements/compounds are called COEFFICIENTS and are the ONLY VALUES YOU CAN CHANGE.

The small numbers to the right of the elements are called SUBSCRIPTS and MUST STAY THE SAME in the equation.

In this example, we want the number of Mg (Magnesium) on the LEFT of the arrow to be the same on the RIGHT of the arrow.

We also want the number of O (Oxygen) to be the same number on both the LEFT and RIGHT of the arrow.

Once we count up the Mg and O on both sides, we can see what needs to change.

We CANNOT TAKE ANYTHING AWAY.

We can ONLY ADD using coefficients.

You'll see this done in the next slide...

Subscript

• written in front of a chemical formula (2NaCl) or symbol (2Li)

• tells you how many molecules of that substance there are

Coefficient

Coefficient VS Subscript

Some text here about the topic of discussion

• written after a chemical symbol (Cl₂)

• tells you how many atoms of that substance (element) there are

Multiple Choice

How many atoms of Mg are in the following compound: MgF₂

• 0

• 1

• 2

• 3

Multiple Choice

How many atoms of F are in the following compound: MgF₂

• 0

• 1

• 2

• 3

Multiple Choice

How many atoms of Cl are in the following compound: 2NaCl

• 0

• 1

• 2

• 3

Multiple Choice

How many atoms of O are in the following compound: 2Na₂O

• 1

• 2

• 3

• 4

Multiple Choice

How many atoms of Na are in the following compound: 2Na₂O

• 1

• 2

• 3

• 4

Multiple Choice

To balance a chemical equation, we change the _________ .

• coefficients

• subscripts

• types of atoms

• types of compounds

Poll

Are you READY to practice balancing equations?

• Yes, of course!

• Maybe

• I think so

Multiple Choice

When counting atoms in an equation, you ______ the coefficient and subscript.

• add

• subtract

• multiple

• divide

Balancing Chemical Equations

1. Write out the equation on lined paper, and divide it into a chart with one side for the reactants and one side for the products.

2. List the elements on the reactants and the products sides of the chart.

3. Count the atoms on the reactants and the products sides of the equation.

4. Find any unbalanced atoms.

5. Use coefficients to balance the atoms.

   • Only put coefficients before a chemical formula, not in the middle.

   • Only change coefficients, not the formulas of the compounds.

   • Repeat steps 4 and 5 as needed until all atoms are balanced.

6. Check that all atoms are balanced.

​Na + MgF₂    ➔   NaF +   Mg

​Na =

Mg =

F =

​Na =

Mg =

F =

​#1

​Na + MgF₂    ➔   NaF +   Mg

​Na = 1

Mg = 1

F = 2

​Na = 1

Mg = 1

F = 1

Multiple Choice

Is the equation (Na + MgF₂ ➔ NaF + Mg) balanced?

• Yes

• No

​Na + MgF₂    ➔   2NaF +   Mg

​Na = 1

Mg = 1

F = 2

​Na = 1 x 2 = 2

Mg = 1

F = 1 x 2 = 2

​2Na + MgF₂    ➔   2NaF +   Mg

​Na = 1 x 2 = 2

Mg = 1

F = 2

​Na = 1 x 2 = 2

Mg = 1

F = 1 x 2 = 2

Multiple Choice

Is the equation (2Na + MgF₂ ➔ 2NaF + Mg) balanced?

• Yes

• No

​ Mg + HCl    ➔  MgCl₂  +    H₂

​Mg =

H =

Cl =

​Mg =

H =

Cl =

​#2

​ Mg + HCl    ➔  MgCl₂  +    H₂

​Mg = 1

H = 1

Cl = 1

​Mg = 1

H = 2

Cl = 2

​ Mg + 2HCl    ➔  MgCl₂  +    H₂

​Mg = 1

H = 1 x 2 = 2

Cl = 1 x 2 = 2

​Mg = 1

H = 2

Cl = 2

​Cl₂  +     KI    ➔       KCl   +     I₂

​Cl =

K =

I =

​Cl =

K =

I =

​#3

​Cl₂  +     KI    ➔       KCl   +     I₂

​Cl = 2

K = 1

I = 1

​Cl = 1

K = 1

I =2

​Cl₂  +     KI    ➔      2KCl   +     I₂

​Cl = 2

K = 1

I = 1

​Cl = 1 x 2 = 2

K = 1 x 2 = 2

I =2

​Cl₂  +    2KI    ➔     2KCl   +     I₂

​Cl = 2

K = 1 x 2 = 2

I = 1 x 2 = 2

​Cl = 1 x 2 = 2

K = 1 x 2 = 2

I =2

​NaCl   ➔      Na +      Cl₂ 

​Na =

Cl =

​Na =

Cl =

​#4

​NaCl   ➔      Na +      Cl₂ 

​Na = 1

Cl = 1

​Na = 1

Cl = 2

​2NaCl   ➔      Na +      Cl₂ 

​Na = 1 x 2 = 2

Cl = 1 x 2 = 2

​Na = 1

Cl = 2

​2NaCl   ➔     2Na +      Cl₂ 

​Na = 1 x 2 = 2

Cl = 1 x 2 = 2

​Na = 1 x 2 = 2

Cl = 2

​Na + O₂    ➔       Na₂O

​Na = 1

O = 2

​Na = 2

O = 1

​#5

​Na + O₂    ➔      2Na₂O

​Na = 1

O = 2

​Na = 2 x 2 = 4

O = 1 x 2 = 2

​4Na + O₂    ➔      2Na₂O

​Na = 1 x 4 = 4

O = 2

​Na = 2 x 2 = 4

O = 1 x 2 = 2

​Na + HCl    ➔    H₂   +    NaCl 

​Na =

H =

Cl =

​Na =

H =

Cl =

​#6

​Na + HCl    ➔    H₂   +    NaCl 

​Na = 1

H = 1

Cl = 1

​Na = 1

H = 2

Cl = 1

​Na + 2HCl    ➔    H₂   +    NaCl 

​Na = 1

H = 1 x 2= 2

Cl = 1 x 2= 2

​Na = 1

H = 2

Cl = 1

​Na + 2HCl    ➔    H₂   +   2NaCl 

​Na = 1

H = 1 x 2= 2

Cl = 1 x 2= 2

​Na = 1 x 2 = 2

H = 2

Cl = 1 x 2 = 2

​2Na + 2HCl    ➔    H₂   +   2NaCl 

​Na = 1 x 2= 2

H = 1 x 2= 2

Cl = 1 x 2= 2

​Na = 1 x 2 = 2

H = 2

Cl = 1 x 2 = 2

K + Cl₂    ➔          KCl 

K = 1

Cl = 2

​K = 1

Cl = 1

​#7

K + Cl₂    ➔         2KCl 

K = 1

Cl = 2

​K = 1 x 2 = 2

Cl = 1 x 2 = 2

2K + Cl₂    ➔         2KCl 

K = 1 x 2 = 2

Cl = 2

​K = 1 x 2 = 2

Cl = 1 x 2 = 2

Multiple Choice

How many atoms of C are there in the reactant side of the equation:

CaCO₃ → CaO + 2CO₂

• 1

• 2

• 3

Multiple Choice

How many atoms of C are there in the product side of the equation:

CaCO₃ → CaO + 2CO₂

• 1

• 2

• 3

Multiple Choice

How many atoms of O are there in the reactant side of the equation:

CaCO₃ → CaO + 2CO₂

• 2

• 3

• 4

• 5

Multiple Choice

How many atoms of O are there in the reactant side of the equation:

CaCO₃ → CaO + 2CO₂

• 2

• 3

• 4

• 5

Multiple Choice

Decide of the following equation is balanced or unbalanced: CaCO₃ → CaO + 2CO₂

• balanced

• unbalanced

CaCO₃ → CaO + 2CO₂

Ca = 1

C = 1

O = 3

Ca = 1

C = 2

O = 1 + (2 x 2) = 5

UNBALANCED

Poll

How well do you understand balancing equations?

• Very well

• I need more practice

• I am confused

Multiple Choice

$$FeS\ +\ HCl\ \rightarrow\ FeCl_2\ +\ H_2S\$$  is a ________ chemical equation

• Balanced

• Unbalanced

Multiple Choice

What does the Law of Conservation of Mass state?

• Matter cannot be gained or lost in a chemical reaction.
• Matter can only be lost in a chemical reaction.
• Matter can only be gained in a chemical reaction.
• Matter can be gained and lost in a chemical reaction. 

Multiple Choice

What is the left part of a chemical equation called?
2H_{2 +} O₂ --> 2H₂O

• Reactants
• Products 
• Yields 
• Chemical Equation 

Multiple Choice

What is the right part of a chemical equation called...
2H_{2 +} O₂ --> 2H₂O

• Reactants
• Products 
• Yields 
• Chemical Equation 

Multiple Choice

What is the total number of atoms present in 5Na₃PO₄

• 5
• 40
• 55
• 8

Multiple Choice

How many Mn atoms are found in the following compound?
3Cr(MnO₄)₆

• 3
• 4
• 6
• 18

Multiple Choice

What is the little number after an element in a chemical equation called.
Example: H₂

• Coefficient 
• Subscript
• Atom
• Equation

Multiple Choice

Is the following equation balanced?...
Al + O₂ --> 2Al₂O₃

• Yes!
• No!

Multiple Choice

How many elements are in C₆H₁₂O₆?

• 1
• 2
• 3
• 4

Multiple Choice

Element or compound?
H₂O

• Element
• Compound

Multiple Choice

What is the number before a chemical formula called?
Ex: 2H₂ + O₂ --> 2H₂O

• Coefficient
• Subscript
• Atom
• Equation

Multiple Choice

How many aluminum atoms are in Al₂(SO₄)₃?

• 1
• 2
• 3
• 4

Multiple Choice

In which of these compounds are there twice as many oxygen atoms as hydrogen atoms?

• H₃PO₄
• H₂SO₄
• HClO₃
• H₂O

Multiple Choice

Is the following equation balanced?
4Fe + 3O₂ --> 2Fe₂O₃

• yes
• no

Multiple Choice

Which of the following equations are correctly balanced?

• 12CO₂ +H₂O --> C₆H₁₂O₆ + O₂
• CO₂ + 9H₂O --> C₆H₁₂O₆ + O₂
• CO₂ + H₂O --> 3C₆H₁₂O₆ + O₂
• 6CO₂ + 6H₂O --> C₆H₁₂O₆ + 6O₂

Multiple Choice

How many HCl molecules do you need to balance this equation? 
Mg +  __HCl --->  MgCl₂ + H₂

• 1
• 2
• 3
• 4

Multiple Choice

Balance this equation

_Al +_HCl --> _H₂ +_AlCl₃

• 2,6,3,2

• it's already balanced

• 4,12,3,4

• 2,1,4,5

Multiple Choice

Balance the following equation:

___ H₂+ ___ O₂→___ H₂O

• 1, 1, 3

• 2, 2, 2

• 1, 2, 1

• 2,1, 2

Multiple Choice

Balance the following equation:

___ SeCl₆+ ___ O₂→___ SeO_{2+____}Cl₂

• 1, 1, 1, 3

• 2, 1, 2, 1

• 1, 2, 1, 2

• 2, 2, 2, 4

Multiple Choice

The group number tells us how many _________ there are in an element.

• groups
• valence electrons
• energy levels
• chemicals

Multiple Choice

True or False - An energy level has to be full before moving on to the next energy level?

• true
• false

Multiple Choice

What is the standard unit of mass at the atomic level?

• centimeters
• millimeters
• amu
• milligrams

Multiple Choice

What is an atom which has gained or last electrons called?

• isotope
• atom
• ion
• balanced

Multiple Choice

What is the octet rule?  How many valence electrons can the first three periods hold?

• 8
• 2
• 2 8 8
• 2 8 16

Multiple Choice

$$FeS\ +\ 2HCl\ \rightarrow\ FeCl_2\ +\ H_2S\$$  is a ________ chemical equation

• Balanced

• Unbalanced

Multiple Choice

$$CH_4\ +2O_2\ \rightarrow\ CO_2\ +2H_2O$$   is a ________ chemical equation

• Balanced

• Unbalanced

Multiple Choice

$$CH_4\ +O_2\ \rightarrow\ CO_2\ +2H_2O$$   is a ________ chemical equation

• Balanced

• Unbalanced

Multiple Choice

$$FeCl_3\ +Na_3PO_4\ \rightarrow\ NaCl\ +FePO_4$$   is a ________ chemical equation

• Balanced

• Unbalanced

Multiple Choice

$$FeCl_3\ +Na_3PO_4\ \rightarrow\ 3NaCl\ +FePO_4$$   is a ________ chemical equation

• Balanced

• Unbalanced

Multiple Choice

$$HCl\ +\ NaOH\ \rightarrow\ NaCl\ +H_2O$$   is a ________ chemical equation

• Balanced

• Unbalanced

Multiple Choice

$$HCl\ +\ 4NaOH\ \rightarrow\ NaCl\ +H_2O$$   is a ________ chemical equation

• Balanced

• Unbalanced

Multiple Choice

A ________ chemical equation contains an equal number of reactant and product atoms.

• Balanced

• Unbalanced

Multiple Choice

An ________ chemical equation contains an unequal number of reactant and product atoms.

• Balanced

• Unbalanced