Chemical Reactions
DESCRIBING CHEMICAL REACTIONS
Learning Targets
You will:

Identify if a chemical
reaction has occurred.

Write a balanced chemical
equation from a chemical
reaction sentence or word
problem.
How is cooking muffins like a chemical
reaction?

Cooking food always involves a
chemical reaction.

Ingredients are mixed and
produce muffins.


Reactants yield products
Chemists use a chemical equation
to convey as much information as
possible about what happens in a
chemical reaction.
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Word Equations

Reactants are written on the
left and separated by plus
signs

Products are written on the
right and separated by plus
signs

An arrow separates the
reactants and products

The arrow reads as yields,
gives, or reacts to produce
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Tips

MUST have correct nomenclature

REMEMBER diatomic molecules

Leave space for coefficient in front of each reactant and
product

Use physical states and symbols when applicable

Most elements are solid in natural state

Bromine and mercury are liquid in natural state

Hydrogen, nitrogen, oxygen, fluorine, chlorine and noble
gases are gas in natural state
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Example
Hydrochloric acid reacts with solid sodium hydrogen
carbonate. The products formed are aqueous sodium
chloride, water, and carbon dioxide gas. Write an unbalanced
equation for this chemical reaction.

__ HCl (aq) + __ NaHCO3 (s)  __ NaCl (aq) + __ H2O (l) + CO2 (g)
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Try on your own

Write a sentence that describes
this chemical reaction:
__ Na (s) + __H2O (l)  __ NaOH (aq) + __ H2 (g)

Solid sodium reacts with liquid
water to produce aqueous
sodium hydroxide and hydrogen
gas.

Sulfur burns in oxygen to
form gaseous sulfur dioxide.
Write an unbalanced
equation for this chemical
reaction.
__ S (s) + __ O2 (g)  __ SO2 (g)
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Try on your own again …

Solid mercury (II) oxide
decomposes to produce
mercury and oxygen.
__ HgO (s)  __ Hg (l) + __ O2 (g)

Carbon reacts with oxygen to
form gaseous carbon dioxide.
__ C (s) + __ O2 (g)  __ CO2 (g)
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Balancing Chemical Equations

The law of conservation of mass states that
mass is neither created nor destroyed.

In order to show that mass is conserved
during a reaction, a chemical equation
must be balanced.

Coefficients are used to balance a
chemical equation — small whole numbers
that are placed in front of the formulas in
an equation in order to balance it.

MUST be in simplest whole number ratio!
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Balancing activity
1.
Obtain an iPad and go to the following link,
https://phet.colorado.edu/
2.
Search and select “balancing chemical equations” simulation
3.
Hit play and work through the introduction

Work through make ammonia, separate water and combust methane
4.
When complete with the introduction hit the game icon at the
bottom and work through all three levels
5.
Report your score for each level to me
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Balancing Chemical Equations

No one solid way to balance

Some may:

balance by sight

follow a strict order

make a table
whatever the method, # of atoms going
into the equation should = # of atoms
going out of the equation.
Helpful tips:

H2O may also be thought of as
HOH.

Balance polyatomic ions as groups
ONLY if they exist on BOTH sides of
the equation

Leave hydrogen and oxygen last
to balance (ESPECIALLY true
w/combustion reactions)
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Example
Students suspended copper wire in an aqueous
solution of silver nitrate. They noticed a deposit of silver
crystals on the copper wire when the copper reacted
with the silver nitrate. They recorded the equation for
this reaction but didn’t balance it. Balance their
equation:

__ AgNO3(aq) + __ Cu(s) → __ Cu(NO3)2(aq) + __ Ag(s)
2 AgNO3(aq) + __ Cu(s) → __ Cu(NO3)2(aq) + 2 Ag(s)
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Try on your own

Balance the equation:

__ Al (s) + __ O2 (g)  __ Al2O3 (s)
__ Fe2O3 (s) + __ H2 (g)  __ Fe (s) + __ H2O (l)
4 Al (s) + 3 O2 (g)  2 Al2O3 (s)
Fe2O3 (s) + 3 H2 (g)  2 Fe (s) + 3 H2O (l)
Balance the following equation:
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Try on your own again …

1.
2.
3.
Balance the following equations:
1.
2 SO2 (g) + __ O2 (g)  2 SO3 (g)
2.
4 P (s) + 5 O2 (g)  __ P4O10 (s)
3.
2 Al (s) + __ N2 (g)  2 AlN (s)
__ SO2 (g) + __ O2 (g)  __ SO3 (g)
__ P (s) + __ O2 (g)  __ P4O10 (s)
__ Al (s) + __ N2 (g)  __ AlN (s)
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Put it all together …

Write and balance equations for the following
reactions:
1.
Iron metal and chlorine gas react to form solid iron (III)
chloride.
2.
Solid aluminum carbonate decomposes to form solid
aluminum oxide and carbon dioxide gas.
3.
Solid magnesium reacts with aqueous silver nitrate to
form solid silver and aqueous magnesium nitrate.
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
Check yourself …
1. 2
Fe (s) + 3 Cl2 (g)  2 FeCl3 (s)
2. Al2(CO3)3
3. Mg
(s)  Al2O3 (s) + 3 CO2 (g)
(s) + 2 AgNO3 (aq)  2 Ag (s) + Mg(NO3)2 (aq)
You will identify if a chemical reaction has occurred.
You will write a balanced chemical equation from a chemical reaction sentence or word problem.
SUMMARIZE …
You will:

Identify if a chemical
reaction has occurred.

Write a balanced chemical
equation from a chemical
reaction sentence or word
problem.