chapter 11 chemical reactions
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Chapter 11Chemical Reactions
Word Equations
Reactants Products
Law of conservation of mass
Iron + oxygen iron(III) oxide
Hydrogen peroxide water + oxygen
Methane + oxygen carbon dioxide + water
Chemical Equations
Fe + O2 Fe2O3
Skeleton equations show reactants and products but do not give relative amounts
Fe(s) + O2(g) Fe2O3(s)
Physical state can be indicated by (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous solution
Chemical Equations
What is a catalyst? A catalyst is a species
that speeds up the rate of a reaction, but is not consumed.
Balancing Chemical Equations
In a balanced equation, each side must have the same number of atoms of each element.
C(s) + O2(g) CO2
Already balanced! H2(g) + O2(g) H2O(l)
Not balanced. What can we do to balance it?
Creating a bicycle: Frame + wheel + handlebar + pedal bicycle F + W + H + P FW2HP2
However, this does not tell us the quantities of the reactants.
The balanced equation would be: F + 2W + H + 2P FW2HP2
Balancing chemical equations
Rules for Balancing Equations
1. Determine the correct formulas for all reactants and products
2. Write reactants on the left and products on the right (skeleton equation)
3. Count the number of atoms of each element in the reactants and products
Rules for Balancing Equations
4. Balance the elements 1 at a time using coefficients. It is best to begin with elements that appear only once on each side of the equation. Do not change subscripts!
5. Check each atom or ion to be sure that it is balanced
6. Make sure that the coefficients are in the lowest possible ratio that balances
Examples
Problem:
AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + Ag(s)
Answer:
2AgNO3(aq) + Cu(s) Cu(NO)3(aq) + 2Ag(s)
TYPES OF
Chapter 11
Reaction TypesThe five general types
of reaction are
• Combination• Decomposition• Single-replacement• Double-replacement• Combustion
Combination Reactions
• Two or more substances form a single new substance
• An example is 2Mg + O2 2MgO• We can represent combination reactions as A + B AB • Complete and balance the following
combination reaction: Be + O2 • Answer: 2Be + O2 2BeO
Decomposition Reactions• A single compound breaks down into two
or more simpler products• An example is 2HgO 2Hg + O2
• We can represent combination reactions as AB A + B• Complete and balance the following
decomposition reaction: HI • Answer: 2HI H2 + I2
Single Replacement• One element replaces another element from a compound
• An example is 2K + 2H2O 2KOH + H2
• We can represent single replacement reactions as
A + BC AC + B• Complete and balance the following single replacement
reaction:
Zn + Ag(NO3)
• Answer: Zn + 2Ag(NO3) 2Ag + Zn(NO3) 2
Double Replacement How would we show the general
equation for a double replacement? (Use A,B,C, and D)
Double replacements consist of ionic compounds (charges must equal zero)
Therefore: AB + CD AD + CB
Double Replacement An example of a double replacement reaction:
K2CO3 + BaCl2 2KCl + BaCO3
Notice that the cations and anions exchange places
Combustion Finally, a combustion reaction is easy
to identify because it usually involves a hydrocarbon reacting with oxygen to form water and carbon dioxide.
Example: CH4 + 2O2 CO2 + 2H2O What is CH4? Why does oxygen exist as a diatomic
molecule?
Predicting Products
What are some clues that might help you to predict the products of reactions?
PRACTICE
Complete and balance the reaction:
Al + Cl2 What type of reaction is it? Do the same for the following
Mg + Cl2
C2H2 + O2
Reactions in Aqueous Solution
70 % Earth’s surface is water
66 % Human body is water
Chemistry in water is very important.
Net Ionic Equations
When the same ionic compounds dissolve in water, they dissociate into ions.
For example, NaCl becomes NA+ and CL-
AgNO3 becomes Ag+ and NO3-
Complete Ionic Equation
A complete ionic equation shows dissolved ionic compounds as dissociated free ions.
Ag+ (aq) + NO-3(aq) + Na+
(aq) + Cl-(aq) AgCl(5) +
Na +(aq) + Cl-
(aq)
…continued Ions that appear unchanged on both side of the
equation may be cancelled out. So, Ag+
(aq) + Cl-(aq) AgCl(5)
The new equation is the net ionic equation Na+
(aq) + NO-3 (aq) are known as spectator ions.
Examples
Pb(5) + AgNO3(aq) Ag (5)+Pb(NO3)2
NO-3(aq) is the spectator ion
Net ionic equation: Pb(5) + Ag(aq) Ag(5)
+ Pb2+(aq)
Balance the equation with respect to mass & charge.
Pb(5) + 2Ag+(aq) 2Ag(5)+Pb2+
(aq)
Predicting Precipitates
You can predict the formation of a precipitate by using solubility rules.
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