Page 18 - Science Course 3 (Book 2)

Signs of a Chemical Reaction Mo8-L2a: How to Recognize Chemical
Reactions?
Lesson 2

In this topic, you will learn the following
lessons:
Mo.8–L2a: How to Recognize Chemical
Reactions?
Mo.8–L2b: Why is Mass Conserved in a
Chemical Reaction?

How to Recognize Chemical
Mo8–L2a
Reactions?
KEY CONCEPTS: Signs of a Chemical Reaction
1. What are some signs that a chemical reaction
might have occurred? During a chemical change, one or more substances
2. What happens to atoms during a chemical change into new substances.
reaction?
A chemical reaction is a process in which atoms of
one or more substances rearrange to form one or
Vocabulary A-Z more new substances.

Let us learn some vocabulary

chemical reaction

a process in which atoms of one or more
substances rearrange to form one or more
new substances.

3 hydrogen 1 nitrogen 2 ammonia Changes in the physical properties of color, state
molecules molecule molecule of matter, and odor are all signs that a chemical
(6 N atoms) (2 N atoms) (2 N 6 H atoms) reaction might have occurred.

If substances get warmer or cooler or if they give off
light or sound, it is likely that a chemical reaction has
Let’s Begin occurred.

Changes in Matter

A physical change does not produce new substances.

For example, water molecules are always made up
of two hydrogen atoms bonded to one oxygen atom
regardless of whether they are solid, liquid, or gas.

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