Chemical Equations and Reactions

Chemical Equations
and Reactions
Describing Chemical Reactions
Describing Chemical Reactions
What are some signs that a
chemical reaction is occurring?
Indications of a Chemical Reaction
• In a chemical reaction, one or more substances
are changed into one or more NEW
• Indications of a chemical reaction include
signs that a new substance has formed.
Indications of a Chemical Reaction
1. Evolution of heat and/or light
Indications of a Chemical Reaction
2. Production of a gas
Vinegar + baking soda
Indications of a Chemical Reaction
3. Formation of a precipitate
(NH4)2S(aq) + Cd(NO3)2 (aq)
Indications of a Chemical Reaction
4. Color Change
Phenolphthalein + NaOH
Writing Chemical Equations
Solid sodium oxide is added to water at room
temperature and forms sodium hydroxide (dissolved
in water).
Write the word equation:
Sodium oxide + water  sodium hydroxide
Write the formula equation:
Na2O(s) + H2O(l)  2 NaOH(aq)
Write formula equations for each of
the following chemical reactions.
1. Hydrogen peroxide in an aqueous solution
decomposes to produce oxygen and water.
2. Solid copper metal reacts with aqueous silver nitrate
to produce solid silver metal and aqueous copper (II)
3. Solid zinc metal reacts with aqueous copper (II)
sulfate to produce copper metal and aqueous zinc
Translating Chemical Equations
PbCl2 (aq) + Na2CrO4 (aq)  PbCrO4 (s) + 2 NaCl(aq)
Write a sentence explaining the above reaction:
Aqueous solutions of lead (II) chloride and sodium
chromate react to form a precipitate of lead(II)
chromate and aqueous sodium chloride.
Translate the following into
1. 2 ZnO(s) + C(s)  2 Zn(s) + CO2 (g)
2. Na2O(s) + 2 CO2 (g) + H2O(g)  2 NaHCO3 (s)
Write and balance equations for
each of the following reactions:
1. Calcium metal reacts with water to form
aqueous calcium hydroxide and hydrogen gas.
2. Nitrogen dioxide gas reacts with water to form
nitric acid and nitrogen monoxide gas.
3. Potassium chlorate decomposes to form
potassium chloride and oxygen.
Classification of Reactions
Today’s objective: Classify reactions according
to five general types:
• Synthesis
• Decomposition
• Single replacement
• Double replacement
• Combustion
1. Iron corrodes in the presence
of oxygen forming iron (III)
General Form:
2. Ammonia is formed by the
combination of nitrogen and
hydrogen at high
temperatures and pressure.
Burning Magnesium video
3. The electrolysis of water
results in the formation of
hydrogen and oxygen.
4. When heated, sodium
bicarbonate decomposes to
sodium carbonate, water, and
carbon dioxide.
Decomposition of HgO
General Form:
Single Replacement
5. When Magnesium is added to
an aqueous solution of copper
(II) chloride, a precipitate of
copper is formed along with a
solution of magnesium
General Form:
6. Sodium reacts violently with
water, resulting in the
formation of sodium
hydroxide and hydrogen gas.
Thermite Reaction
Double Replacement
7. When aqueous solutions of
potassium iodide and lead (II)
nitrate are mixed, a solid
precipitate forms: lead (II)
General Form:
8. Hydrochloric acid is neutralized
by addition of a base (sodium
hydroxide) resulting in the
formation of water and a salt.
Potassium iodide + lead (II) nitrate
9. Ethanol (C2H5OH) burns in
oxygen, producing carbon
dioxide and water.
General Form:
10. Welders use acetylene
(C2H2) torches. The flame is
produced as acetylene burns
in the presence of oxygen.
Burning Gasoline and Ethanol
Using the Activity Series
Zn(s) + H2O(l)  no reaction
Sn + O2  SnO2
Cd + Pb(NO3)2  Cd(NO3)2 + Pb
Cu + HCl  no reaction
Will the following reactions occur?
MgCl2 (aq) + Zn(s)
Al(s) + H2O(g) 
Cd(s) + O2 (g) 
I2 (s) + KF 

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