Download Chapter 7 Chemistry Aya

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Ch. 7 Chemical Reactions: An Introduction
Aya Abdellatif, Amanda Kang, Ishrat
Mannan, Moriah Smith
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Section 1 : Evidence for a
Chemical Reaction
 Chemical
Reaction: A change in which
a substance is changed into one or more
new substances.
 Chemical
reactions are not always
visible
 Change
in temperature and/or heat
being produced or absorbed can
indicate a chemical reaction
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Section 1 Cont.
 You
can often tell if a chemical reaction has
occurred by visual clues given :
 General Clues Are:
 A flame is produced
 Color change
 Bubbles are produced
 A solid forms
 More Specific Examples
 Hair changing colors
 Metal rusting
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Section 2 : Chemical Equations
 Chemical
reaction : when one or more
substances are changed into one or more new
substances by the reorganization of component
atoms
 Chemical
equations : a representation of a
chemical reactions using the formulas of the
starting substances that react (reactants) and the
new substances that are formed (products)
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Section 2 Cont.
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In a chemical reaction, atoms are neither created nor destroyed
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All atoms present in the reactants must be accounted for among
the products
 Making sure that the equation for a reaction obeys this rule is
called balancing the chemical equations
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Balanced chemical equation : shows the actual numbers of
molecules involved in this equation
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In the equation the physical state the of reactants and products
are indicated:
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Solid (s)
Liquid (l)
Gas (g)
Dissolved in solution/ Aqueous solution (aq)
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Section 3 : Balancing Chemical
Equations
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Atoms are conserved in a chemical reaction
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The same number of each type of atom is found in the
reactants and products
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The formulas of the compound must never be changed in
balancing a chemical equation
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Coefficient: the number written in front of the chemical
formulas in a balanced chemical equation that indicate the
relative numbers of reactants and products in the reaction
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Placing coefficients in front of the formula is how to balance
an equation
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How to Write a Balanced Equation
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Step 1: Read the description of the chemical reaction
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State the reactants, products and their states
Write appropriate formula
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Step 2: Write unbalanced equation
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Step 3: Balance the equation
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Proceed element by element to determine what coefficients are
needed so that there is an equivalent number of atoms on the reactant
and product side
don’t change the formulas of any of the reactants or products
Step 4: Check and make sure that the coefficients used give the
same number atoms on both sides of the equation
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Make sure that the coefficients used are the smallest whole number
by determining whether or not all the coefficients can be divided by
the same whole numbers to get a smaller set of whole numbers.
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Situation #1
Solid
Potassium reacts
with liquid water to form
gaseous hydrogen and
potassium hydroxide
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Situation #2
Ammonia
gas reacts
with oxygen gas to
produce gaseous water
and nitrogen monoxide
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Quiz Time!
1.List two examples of how you can visually tell if a chemical
reaction has occurred.
2.Write down a real-life example of a chemical reaction.
3.True or false. A chemical reaction is when one or more
substances are changed to make new substances.
4.Fill in the blank; In a chemical reaction, atoms are netither
______ or _______
5.Briefly explain in one sentence the rule of balancing
chemical equations.
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Quiz time, continued
6.Write how solids, liquids, gases, and dissolved in
solution/Aqueous.
7.For balancing an equation, the same number of each type of
atom is found in the _____ and ______.
8.________ is the number written in front of the chemical
formulas in a balanced equation.
9. What are the steps 1-3 of writing a balanced equation?
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Answers
1.Possible answers: flame is produced, color change, bubbles
are produced, solids are formed.
2.Answers vary
3. True
4. Created or destroyed
5. Basically, all atoms present in the reactants must be
accounted for among the products.
6.(s)(l)(g)(aq)
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Answers cont.
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7. reactants and products
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8.Coefficient
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9.Step 1: Read the description of the chemical reaction. Step
2: Write unbalanced equation. Step 3: Balance the equation.
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