Introduction to Chemical Equations and Reactions

Intro To Chemical Reactions

​We Will
1) What is a Chemical Reaction
2)Chemical Equations
3)Indications of a Chemical Reaction
4) Law of Conservation and application
I will apply my understanding.

A chemical reaction is the
process by which one or

more substances are

changed into one or more

different substances.
(aka chemical change)

Multiple Choice

When a new substance forms as a result of a chemical reaction, what type of change has occurred?

• Chemical Change

• Physical Change

Multiple Choice

The process by which one or more substances change to produce one or more different substances

• Chemical Process

• Reactant

• Chemical Reaction

Bonds between atoms of
substances are broken, atoms are
rearranged, and new bonds are
formed—forming new substances
with different properties!

A chemical reaction is

represented by a

chemical equation.

Reactant:

✔ substances that combine
✔ substances to the left

In any chemical reaction, the
original substances are known as
the reactants . . .

Two parts of a

chemical equation

Multiple Choice

What are Chemical Reactions?

• It's when you mix substances.
• a process in which atoms rearrange to form new substances
• When something bubbles.

Product:

✔ substances formed
✔ substances to the right

Two parts of a

chemical equation

. . . and the resulting substances are
know as the products.

Multiple Choice

What is the right part of a chemical equation called?

2H₂ + O₂ ---> 2H₂O

• Reactants

• Products

The arrow (➔) separates the reactants from the
products. (Read as “yields”)

Chemical Equations

Represent a reaction in writing

2H2 + O2 ➔ 2H2O

• Energy change (Heat, Light)

• Production of gas (bubbles, fizz, smoke)

• Change in color

• Formation of a precipitate

​Indications of a Chemical Reaction

Multiple Choice

You know you a chemical reaction has occurred if 

• there is a precipitate.
• there is a color change.
• there is a temperature change.
• All of these answers are evidence.

A solid that is produced
as a result of a chemical
reaction in solution and
that separates from the
solution is known as a
precipitate.

​Precipitate

Multiple Choice

Which of the following describes a precipitate?

• a liquid forms when a block of metal is heated
• a solid forms when one liquid is poured into another
• bubbles form when an acid is poured on a rock

Change of state or phase is a
physical change. (melting,
freezing, condensing, etc…)
The same substance is still
present – just in a different
physical state.

Dissolving something is
a physical change. The
substance is still
present- just dissolved in
a solvent. It can be
separated!

Atoms are neither created nor destroyed in
ordinary chemical reactions. (just
rearranged)

•Same number of atoms of each element
must appear on both sides of the
equation.

• For an equation to correctly
describe a reaction, it must be “balanced.”

​Law of Conservation of Mass

According to the law of
conservation of mass, the total
mass of reactants must equal
the total mass of products for
any given chemical reaction.

Multiple Choice

Which of the following describes the law of conservation of mass?

• In a reaction, atoms are not lost or made.
• In a reaction, mass never stays the same.

Before we begin balancing
chemical equations, we must
know how to use coefficients.

A coefficient is a whole
number that appears in front
of a formula in a chemical
equation.

• Coefficients are numbers placed in

front of a symbol or formula and are
used to balance an equation.

• Example:

H2 + O2🡪 H2O
2 H2 + O2🡪 2 H2O

• Never alter a subscript when trying to

balance a chemical equation.

​Using Coefficients

2H2O

Coefficient
(# molecules)

Subscript
(#atoms)

Number of Atoms =

(subscript) x (coefficient)

If there is no coefficient, it
is understood to be one (1)

Multiple Choice

2 H₂SO₄

• 4 H, 2 S, 8 O

• 4 H, 2 S, 6 O

4 Si2H3

8 Si
12 H

Multiple Choice

4 Si₂H₃

• 8 Si and 12 H

• 4 Si and 4 H

• 6 Si and 7 H

2 H2SO4

4 H
2 S
8 O