Chemical Reactions
Chemical Reactions
• 10.1 Reactions and Equations
• Evidence of Chemical Reactions.
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• The process of which the atoms of one or more substances are
rearranged to form different substances is called a Chemical
Reaction.
•
• Evidence of a Chemical Reaction
• 1. color change
• 2. formation of a solid (including smoke), liquid or gas
• 3. energy is released or absorbed (temp change), also gives off
light, noise
• 4. odor
Representing Chemical Reactions
• Chemical Equations- are statements that
chemists use to represent chemical reactions
• They show:
• Reactants- the starting substances
•
• Products- the substances formed during a
reaction
Symbols
• Chemical equations show
the direction in which a
reaction takes place, so, an
arrow is used rather than
an equals sign. You read
the arrow as “react to
produce” or “yield”.
Word Equations
• Word equations describe the reactants and
products of chemical reactions.
• Ex. reactant1 + reactant 2  product 1
•
• iron(s) + chlorine(g)  iron(III) chloride(s)
•
• This equation is read: iron and chlorine react
to produce iron(III)chloride
Skeleton Equations
• A skeleton equation uses chemical formulas
rather than words to identify the reactants
and the products.
• Ex: iron(s) + chlorine(g)  iron(III) chloride(s)
•
Fe(s) + Cl2(g)  FeCl3 (s)
Writing Ionic Compound Formulas
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Review.
1. Write the symbols
2. Write the charges
3. Cross the charges from top to bottom.
4. Remove the charges
5. Simplify the numbers (ratios) and remove
the ones.
• Reminder: treat polyatomic ions as one ion.
Balancing Chemical Equations.
The law of conservation of matter states that, in
a chemical change, matter is neither created nor
destroyed.
Balancing Chemical Equations.
Chemical equations must
show that matter is
conserved during a
chemical reaction. Such
an equation is called a
balanced equation.
Balancing Chemical Equations.
To balance an equation you must find the
correct coefficients for the chemical formulas in
the skeletal equations. A coefficient in a
chemical equation is the number written in
front of a reactant or product.
Balancing Chemical Equations.
Coefficients are whole numbers and are not
written if the value is 1. In a balanced equation,
coefficient is the lowest whole-number ratio of
the amounts of all the reactants and products.
Steps for Balancing Equations
• 1. Write the skeletal equation for the reaction.
• 2. Count the atoms of the elements in the
reactants.
• 3. Count the elements in the products.
• 4. Change the coefficients to make the number
of atoms of each element equal on both
•
sides of the equation.
• 5. Write the coefficients in their lowest possible
ratio.
• 6. Check your work.
Steps for Balancing Equations
• 1. Write the skeletal equation for the
reaction.
Steps for Balancing Equations
• 2. Count the atoms of the elements in the
reactants.
Steps for Balancing Equations
• 3. Count the elements in the products.
Steps for Balancing Equations
• 4. Change the coefficients to make the
number of atoms of each element equal on
both
Steps for Balancing Equations
• 5. Write the coefficients in their lowest
possible ratio.
• Ratio is 1:1:2; so it is the lowest possible ratio
Steps for Balancing Equations
• 6. Check your work.
• Make sure the chemical formulas are
written correctly.
• Check that the number of atoms is equal on
both sides.
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Recommended order of balancing
1. Metals
2. Non-metals
3. Polyatomic ions
4 Oxygen and hydrogen
• MgCl2 + Na2O  MgO + NaCl
Try to balance these equations!
Do Now
• In your packet: Write a skeletal equation of
the following reactions and then balance.
• FeCl3(aq) + 3NaOH  Fe(OH)3(s) + 3NaCl(aq)
• CS2(L) + 3O2(g)  CO2(g) + 2SO2(g)
• Zn(s) + H2SO4(aq)  H2(g) + ZnSO4(aq)
Classifying Chemical Reactions
Synthesis Reaction
• When two elements or substances react it is
always a synthesis reaction.
• A + B  AB
Synthesis Reaction
Classifying Chemical Reactions
Combustion Reaction
• In combustion reactions, oxygen combines
with a substance and releases energy in the
form of heat and light.
• Ex
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Decomposition Reactions
• A decomposition reaction is one in which a
single compound breaks down into two or
more compounds or elements.
• AB  A + B
Decomposition Reactions
• AB  A + B
• Decomposition reactions often require an
energy source such as heat or electricity, to
occur.
Replacement Reactions
Single Replacement Reactions
• In a single-replacement reaction, the atoms of
one element replace the atoms of another
element in a compound.
• A + BX  AX + B
Replacement Reactions
• Single Replacement Reactions
• A + BX  AX + B
Replacement Reactions
• Single Replacement Reactions
• A + BX  AX + B
• You can use the Activity Series Chart to predict
if a single replacement reaction
will
occur.
• A specific metal can replace any
metal
listed below it.
• It cannot replace any metal listed
above it.
Single Replacement Reactions
Replacement Reactions
• Double Replacement Reaction
• In a double replacement reaction ions are
exchanges between two compounds.
Replacement Reactions
• A solid produced during a chemical reaction is
called a precipitate.
• A double replacement reaction will produce
either a precipitate, a gas, or water.
• You can predict which ions will form a
precipitate by using a solubility table.
Classifying Chemical Equations
__B__ 1. A + B  AB
a. Decomposition Reaction
__C__ 2. A + BX  B + AX
b. Synthesis Reaction
__D__ 3. AX + BY  AY + BX
c. Single Replacement
Reaction
__E__ 4. CxHy + O2  CO2 + H2O
d. Double Replacement
Reaction
__A__ 5. AB  A + B
e. Combustion Reaction
Types of Reactions
http://www.youtube.com/watch?v=tE4668aarck
http://www.youtube.com/watch?v=aAWcCQB75d0
Synthesis Reaction
A + B  AB
• Decomposition Reactions
AB  A + B
• Combustion Reaction
Replacement Reactions
• Single Replacement
• A + BX  AX + B
• Double replacement
• AX + BY  AY + BX
Do Now
1. CO2  C + O2
2. CH4 + O2  CO2 + 2H2O
3. NaCl + AgNO3  AgCl + NaNO3
4. S + Cl2  SCl2
5. Zn + 2HCl  ZnCl2 + H2
• 27. synthesis, combustion, decomposition, single
replacement, double replacement.
• 28. Oxygen combines with a substance and
releases energy in the form of heat and light.
• 29. In a single replacement reaction, atoms of
one element replace atoms of another element in
a compound. In a double replacement reaction
two compounds dissolved in water exchange
positive ions.
• 30. Double replacement reactions produce
two different compounds, one being a solid
precipitate, water or gas.
• 31. The reaction does occur because nickel is
more reactive than gold.
• 32. A synthesis reaction will likely occur.
Ba + F2  BaF2
Reactions in Aqueous Solutions
• An aqueous solution is
substance dissolved in
water. A substance
dissolved in a solution is
called a solute. The
substance that dissolves
a solute to form a
solution is called a
solvent.
• In an aqueous solution
the solvent is water.
• Reactions that Form Precipitates
• A precipitate is a solid produced in a chemical
reaction in a solution.
• You can predict if a solid is formed in a double
replacement reaction by using a solubility
chart.
• Simply pick the compound that does not
dissolve in water.
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