Chemical Reactions
Standards

Conservation of Matter and Stoichiometry
3a. Students know how to describe chemical
reactions by writing balanced equations
Objectives

Identifying the reactants, products and other parts of
chemical equations

Write word equations from a chemical reaction
description

Write chemical equations from word equations

Identify and include solid (s), liquid (l), gas (s), and/or
aqueous (aq) in chemical equations

Identify and write the seven diatomic elements
Definitions

Chemical equation: a precise detailed accounting of
both the identities and amounts of reactants consumed
and products formed in a reaction

Identities: all participants in reaction get named

Amounts: how much is specified in equation, (moles)

Reactants: the starting substance(s) in a chemical
reaction

Product: substance(s) formed in a chemical reaction
Definitions

Word equation: description of a reaction without
using chemical formulas

Reactants: what you start with

Products: what is made
Definitions

Catalyst: a substance that speeds up a
reaction without being used up; enzymes good
example

Aqueous: dissolved in water (aq)

Diatomic: two of the same atom naturally
bound together
Writing a Word Equation

Hydrogen reacts with oxygen to form water

Word Equation:

hydrogen + oxygen → water
Reactants

Chemical Equation:

H2 + O2 →H2O
Product
Diatomic Elements

Diatomic: two of the same atom naturally
bound together

Hydrogen and Oxygen and some others exist
bound together. They are always found as a
pair, so when you write them write them as
H2, O2.
Diatomic Elements “7”
Write the Word & Chemical
Equation…

Calcium metal reacts with chlorine gas
to produce calcium chloride

Calcium + chlorine → calcium chloride

Ca + Cl2 → CaCl2
Write the Word & Chemical
Equation…

When zinc metal reacts with oxygen
gas, solid zinc oxide is formed.

Zinc + oxygen → zinc oxide

Zn + O2 → ZnO
Write the Word and Chemical
Equation…

Carbon dioxide gas and water are
produced when methane gas is burned
in oxygen.

Methane + oxygen → carbon dioxide
+ water

CH4 + O2 → CO2 + H20
Write the Word & Chemical
Equation…

When zinc metal is placed in a solution of
hydrochloric acid, hydrogen gas and a zinc
chloride solution are formed.

Zinc + hydrochloric acid → hydrogen gas
+ zinc
chloride

Zn(s) + HCl (aq) → H2 (g) + ZnCl2 (aq)
Rules for balancing
1.
Must have same # of each atom on both
sides of the equation
2.
Must use coefficients to balance, can not
add subscripts
Balance the Equation

Calcium metal reacts with chlorine gas
to produce calcium chloride

Calcium + chlorine → calcium
chloride

Ca +
Cl2 →
CaCl2
Balance the Equation

When zinc metal reacts with oxygen
gas, solid zinc oxide is formed.

Zinc + oxygen → zinc oxide

Zn +
O2 →
ZnO
Balance the Equation

Carbon dioxide gas and water are
produced when methane gas is burned
in oxygen.

Methane + oxygen → carbon dioxide
+ water

CH4 +
O2 →
CO2 +
H20
Balance the Equation

When zinc metal is placed in a solution of
hydrochloric acid, hydrogen gas and a zinc
chloride solution are formed.

Zinc + hydrochloric acid → hydrogen gas +
zinc chloride

Zn(s) +
HCl (aq) →
H2 (g) +
ZnCl2 (aq)
WORKSHEET a
END