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Chemical Reactions
G.Burgess 2006
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Chemical Reactions
• Occur when atoms of substances join other atoms of other substances to form different chemical materials
• There are several types of chemical reactions
• Chemists show chemical reactions symbolically as chemical equations
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Chemical Equations
NaOH(aq)+ HCl(aq) NaCl(aq) + H2O(l)
Reactants Products
Molecular formula of compound
State
(aq) = aqueous/ in water
(l) = liquid**the ‘+’’s means “reacts with”
**the arrow between the reactants and products means “to give”.
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Types of chemical reactions
1. Formation(synthesis): when two pure substances combine to make a new substance
ie. 2H2 + O2 2H2O
2. Decomposition: when a compound breaks up into its individual parts.
ie. 2H2O 2H2 + O2
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Types of chemical reactions
3. Single displacement: when one element is removed from a molecule and replaced by another element.
ie. 2Fe + 6HCl 2FeCl3 + 3H2
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Types of chemical reactions
4. Double displacement: When 2 molecules switch elements.
AgNO3 + HCl AgCl + HNO3
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Review
1. Fe + S FeS
2. 2 Mg + O2 2 MgO
3. Na2O + H2O 2 NaOH
4. CuCO3 CuO + CO2
5. Fe + H2SO4 FeSO4 + H2
6. AgNO3 + NaCl AgCl + HNO3
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Answers to review
1. Synthesis
2. Synthesis
3. Synthesis
4. Decomposition
5. Single Displacement
6. Double displacement
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Rules of chemical reactions
• Law of conservation of matter:– The number of atoms of each
element produced is the same as the number of atoms in the reactants.
ie. H2 + O2 H2O
2H2 + O2 2H2O
Creating a balanced equation helps demonstrate this law.
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Balancing Chemical Equations
• All chemical equations must demonstrate the Law of conservation of matter.
• Begin by balancing the metals• Then Poly atomic ions• Then non-metals• Then hydrogen• Lastly, balance oxygen.
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Balancing Chemical Equations
Example:Al + O2 Al2O3
1. Al on the left = 1; Al on the right = 2. Put a 2 in front of the Al on the left.2Al + O2 Al2O3
2. O on the left = 2; O on the right = 3. Put a 3 in front of O on the left and 2 in front of Al on the right.2Al + 3O2 2Al2O3
NOTICE: The Al’s do not match. To balance the Al’s use a multiple of all three numbers (2Al=2; 2Al2=4) Since Al = Al1 and 1*4 = 4. then the balanced formula is…4Al + 3O2 2Al2O3
**Now we have 4Al’s and 6O’s on each side.
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Review
1. S + H2SO4 SO2 + H2
2. NaCl + BeF2 NaF + BeCl2
3. Ca(OH)2(aq) + HCl(aq) CaCl2(aq) + H2O(l)
4. CH4 + O2 CO2 + H2O
5. Mg + Mn2O3 MgO + Mn