• Describe the components of a chemical equation in order to
determine what occurs during a chemical reaction.
Chemistry
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• To show the change of reactant(s) into product(s), we write a
chemical equation.
• A chemical equation uses chemical formulas, numbers,
mathematical symbols and arrows to show what happens
during the chemical reaction.
• The chemical equation below shows the change of hydrogen
peroxide (H2O2) into water (H2O) and oxygen (O2).
Chemistry
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© Stephanie Elkowitz
• There are 2 sides to a chemical equation:
– The substances to the left of the arrow are the reactants. These are the
substances that undergo the chemical change. We call this side of the
equation the “left side” of the equation.
– The substances to the right of the arrow are the products. These are
the substances that form as a result of the chemical change. We call
this side of the equation the “right side” of the equation.
Left Side: Reactants
Chemistry
Right Side: Products
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© Stephanie Elkowitz
• If there is more than one reactant, an addition sign (+) is used
to show all the reactants of the chemical reaction.
• If there is more than one product, an addition sign is also used
to show all the products.
Addition sign (+)
means “and”
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• Numbers in front of a chemical formula indicate how many
molecules are involved in a chemical reaction.
• If there is no number in front of a chemical formula, only one
molecule of that substance is involved in the chemical
reaction.
No number indicates
only 1 molecule
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© Stephanie Elkowitz
• The arrow symbolizes the direction of the chemical reaction.
• A
symbolizes a reaction that occurs in one direction.
• A reaction with an arrow like this is usually irreversible. Once
the reactants change into the products, the products cannot
change back into the reactants.
This reaction
occurs in one
direction
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© Stephanie Elkowitz
• A
symbolizes a reaction that occurs in either direction.
• A reaction with an arrow like this one is reversible. The
reactants can change into the products and the products can
change into the reactants.
• Environmental conditions and other factors determine the
direction of the reaction.
This reaction
can occur in
either
direction
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© Stephanie Elkowitz
• Sometimes symbols are used in a chemical equation to show
the state of matter of each substance.
• These symbols are placed in parentheses to the right of the
chemical formula of each substance.
– (s) stands for solid
– (l) stands for liquid
– (g) stands for gas
• Usually a precipitate (solid) or bubbles (gas) form when there is
a change in state of matter.
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© Stephanie Elkowitz