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TRANSCRIPT
Chapter 9 Part 1 : Types of
Chemical Reactions
5 common
Reaction types:
Reaction Types 1. Composition reactions
a.k.a. synthesis or
combination reactions
•A + B AB
Composition (Synthesis)
Reactions
composition Examples:
2H2 (g) + O2 (g) 2H2O (l)
CaO(s) + H2O(l) Ca(OH)2(aq)
2. Single Replacement
Reactions
• Metal replaces another metal
• C + AB A + CB
Or…
• nonmetal replaces another
nonmetal
• C + AB B + AC
Single-Replacement Reactions
• SR Examples:
Pb + 2HNO3 Pb(NO3)2 + H2
F2 + 2NaI 2NaF + I2
Predict the Products
Zn + CuCl2 ZnCl2 + Cu
3. Decomposition reactions
•When compounds split
up (break down) into 2
or more products
• AB A + B
Decomposition Reactions
Decomp Examples
• CaCO3 CaO + CO2 (g)
• Na2CO3 Na2O + CO2 (g)
4. Double Replacement
Reactions
• AB + CD AD + CB
The ions of two compounds exchange places in an aqueous solution to form two new compounds.
Two ionic compounds “swap” ions.
Double Replacement
Reactions
Usually forms a precipitate
• precipitate: a solid product that is formed when two aqueous solutions are mixed.
AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)
Precipitate
Examples
PbSO4(aq)+2KCl(aq) K2SO4(aq) + PbCl2 (s)
AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)
Predict the Products
H2O
KOH + H2SO4 K2SO4 + HOH
5. Combustion reactions
• CXHY + O2 CO2 + H2O
• Easily recognized when O2 is
one reactant, and CO2 & H2O
are the products
Example
• C3H8 + 5O2 3CO2 + 4H2O
• CH4 + O2 CO2 + H2O
Practice time!!!!!
1) 2Li + 2H2O 2LiOH + H2
single replacement / displacement
2) NH4Cl NH3 + HCl
decomposition
3) AgNO3 + NaCl AgCl + NaNO3
double replacement / displacement
4) 2C6H14 + 19O2 12CO2 + 14H2O
combustion
5) N2 + 3 H2 2 NH3 Composition/synthesis
Chemical Reaction • a change in which one or more substances are converted into new substances – · old bonds break
– · new bonds form
– · atoms are rearranged
Indicators of reactions:
1.Production of heat and/or light.
2.Production of a gas: bubbles in a solution
3.Formation of a precipitate (solid)
4.Color change
Chemical Equation • a way to describe a chemical reaction using chemical formulas and other symbols
• Reactants Products
• (starting material) (new substances)
Common Symbols used in Equations
= yields, forms, produces, makes, etc
(s) solid state or precipitate
(l) liquid state
(g) gaseous state
(aq) aqueous state (dissolved in water)
: heat is applied (placed over the arrow)
catalyst (also written over the arrow)
substance that speeds up a chemical reaction without becoming part of the reaction.
Diatomic molecules
• 7 diatomic elements (know) H2 O2 F2 Br2 I2 N2 Cl2 - “infamous 7” or “HOFBrINCl”
(If any of these are present in a reaction as a reactant or product they must be shown as diatomic)
Unit 3 – part 1 • balancing equations (eqn)
Significance of Equations
• Coefficients show relative amounts of reactants and products in the equation
• When an equation is balanced it will satisfy the law of conservation of mass
Law of conservation of mass states that:
• Atoms are neither created nor destroyed (in ordinary chemical reactions). – number of atoms on left = number of atoms on right
– In balancing, do not split up compounds or change the formula (subscripts).
– Remember common polyatomic ions and diatomic molecules.
Subscripts vs. Coefficients
• Subscripts tell how many
atoms of an element are in
the compound.
• SUBSCRIPTS CAN NEVER
BE CHANGED!!!!!!!!
• Coefficients are found at the
beginning of a formula, and
indicate the number of moles
present in the equation.
• If no coefficient is written it is one
• Coefficients CAN BE changed in
balancing equations.
Order for Balancing
(recommend making a chart
under the arrow)
1.M - metals (Balance metals first.)
2.I - ions (Balance polyatomic ions.)
3.N – nonmetals (Balance Cl, S, N, etc.)
4.O – oxygen
5.H – hydrogen
To balance combustion Rxn:
CHO (carbon then hydrogen
and oxygen last)
When there are an odd
number of oxygens in the
products, do the “half-trick”
Two Important Principles!!!
• Every chemical compound has a
formula that cannot be altered
(can’t change the subscripts).
• A chemical reaction must account
for every atom used. (Law of
Conservation of Mass)
THE END