Chemical Reactions

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Chemical Reactions
Term 4 – Year 9 Science
Learning Goals
I will understand:
• that chemical reactions occur as a result of the rearranging of
particles.
I will be able to:
• interpret chemical formulae
• write word equations.
Atoms and molecules
• Atoms are individual particles that are made up of a nucleus
and electrons
• Molecules are groups of atoms that form distinct
arrangements of atoms
• Lattices are networks of atoms that make up compounds or
elements
Atoms molecules and lattices
• Noble gases exist as single atoms
e.g. Helium
• Some elements join to form many compounds
or molecules
e.g. water
sugar
• Metals, carbon and many compounds form
lattices. E.g.salt
iron
Chemical formulae
• All pure substances (elements & compounds) can be
represented using chemical formulae
• In a molecule, the formula describes the number of, and types
of atoms (eg H2O, O2)
• In a lattice, the formula describes a ratio of elements (eg Fe,
NaCl, MgCl2)
Magnesium
Chloride
Questions
Determine the number of atoms and the names of elements in
each of the following
• Elements:
• Compounds:
- NaOH
- H2 Hydrogen – 2
- MgCl2
- S8 Sulfur – 8
- H2O2
- C60 Carbon – 60
Nitrogen
–
3
- H2SO4
- N3
Argon – 1
- Ca(OH)2
- Ar
- Mg3(PO4)2
Chemical Reactions
• A chemical reaction occurs when new substances are formed
(ie a chemical change)
• Chemicals that react to cause a chemical change are known as
reactants
• Chemicals that are produced during chemical reactions are
known as products
Word Equations
• A word equation is a straightforward way to represent a
chemical reaction
Reactants→ Products
An example is the reaction between hydrogen and oxygen to
produce water.
hydrogen + oxygen → water
Write word equations for the following
Chlorine + methane
tetrachloride + hydrogen chloride
• When chlorine gas reacts with methane, carbon tetrachloride and
hydrogen chloride are produced.
• When sodium oxide is added to water, sodium hydroxide is produced.
Sodium oxide + water
sodium hydroxide
• In a blast furnace, iron oxide and carbon monoxide gas produce carbon
dioxide gas
iron.
Ironand
oxide
+ carbon monoxide
carbon dioxide + iron
• Sugar reacts with oxygen in cells to produce carbon dioxide and water
Sugar + oxygen
carbon dioxide + water
Model a chemical reaction
• In this activity you will model a chemical
reaction using a molecular model kit.
• The reaction will between hydrochloric acid
and sodium hydroxide
Build your reactants
• Build a hydrochloric acid molecule with one hydrogen atom
and one chlorine atom
• Build a sodium hydroxide molecule with one sodium atom, one
oxygen atom and one hydrogen atom
H
Cl
O
Na
H
Conduct the reaction
• When the two reactants collide, a reaction
occurs.
• The hydrochloric acid breaks apart while the
sodium breaks off the hydroxide particle
H
Cl
O
Na
H
Assemble your products
• Join the hydrogen atom from the hydrochloric acid with the
hydroxide particle (OH)
• Join the sodium atom with the chlorine atom
Na
Cl
O
H
H
Reflection
• What held the atoms of the reactants to each other?
• What did you need to do to the reactants in order to begin
the chemical reaction?
• What did you need to do to the free atoms in order to create
the products?
Chemical Reaction - Definition
“A chemical reaction occurs when chemical
bonds are broken and new bonds are formed,
creating new substances”
Chemical Reactions – Explained
• Molecules are always moving
• Reactions are started when molecules collide and the bonds
are broken
• Molecules need to collide with enough energy or force to
cause bonds to be broken – this is called the activation energy
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