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Chapter 8
Describing Chemical Change Types of Chemical Reactions Reactions in Aqueous Solution
Chapter 8.1 Describing Chemical Change
Word Equations Chemical Equations Balancing Chemical Equations
Word Equations
Reaction – one or more substances (the reactants) change into one or more new substances(the products)
Reactants Products = ?
Yields, gives or reacts
Word Equations
As reactants are converted to products, the bonds holding the atoms together are broken and new bonds are formed.
REMEMBER: The atoms are neither created nor destroyed, just rearranged. (Law of Conservation of Mass)
Word Equations
Rust
Iron reacts with oxygen to produce iron(III) oxide (rust)
Iron + Oxygen Iron(III) Oxide
(reactants) (yields) (products)
Word Equations
Hydrogen peroxide reacts to form water and oxygen gas.
Hydrogen peroxide water + oxygen
MnO2
H2O2(aq) H2O(l) + O2(g)
Word Equations
Burning of Methane
Methane + Oxygen Carbon Dioxide + Water
Chemical Equations
Iron + Oxygen Iron(III) Oxide
Fe + O2 Fe2O3
Now add physical states
Fe(s) + O2 (g) Fe2O3 (s)
Chemical Equations
Reactions with a catalyst Catalyst – a substance that speeds up the
rate of a chemical reaction, but is not used up in the reaction.
A catalyst is written above the arrow
Chemical Equations
Manganese(IV) oxide catalyzes the decomposition of hydrogen peroxide.
Balancing Chemical Reactions
Each side of the equation has the same number of atoms of each element.
C(s) + O2(g) CO 2(g)
1 carbon, 2 oxygen 1 carbon, 2 oxygen
Balancing Chemical Reactions
H2(g) + O2(g) H2O(l)
2 hydrogen, 2 oxygen 2 hydrogen, 1 oxygen
Balance
2 H2(g) + O2(g) 2 H2O(l)
Balancing Chemical Reactions
Rules 1) Determine the correct formulas 2) Write the formulas for the reactants on the
left and the products on the right. Place a in between. If there are two or more reactants or products, use a + in between.
3) Count the number of atoms of each element.
Balancing Chemical Reactions
Rules 4) Balance the elements one at a time until
you have equal numbers of elements on each side
5) Make sure all numbers are in their smallest whole number ratio.
Chapter 8.2 Types of Chemical Reactions
Classifying Reactions Combination Reactions Decomposition Reactions Single-Replacement Reactions Double-Replacement Reactions Combustion Reactions Predicting Products of Reactions
Classifying Reactions
Identify the five general types or reactions: Combination Reactions Decomposition Reactions Single-Replacement Reactions Double-Replacement Reactions Combustion Reactions
Combination Reactions
Two or more substance combine to form a single substance.
General Reaction: R + S = RS
Example: 2Mg(s) + O2(g) 2 MgO(s)
Decomposition Reactions
A single compound is broken down into two or more substances.
General Reaction: RS = R + S
Example: 2HgO(s) 2 Hg(l) + O2(g)
Single-Replacement Reactions(Single Displacement Reactions)
One element replaces a second element in a compound.
General Reaction: T + RS = TS + R
Example: 2K(s) + 2H2O(l) 2KOH(aq) + H2(g)
http://www.kentchemistry.com/links/Kinetics/PredictingSR.htm
Double-Replacement Reactions
Exchange of positive ions between two reacting compounds.
General Reaction: RS + TU = RU + TS R+S- + T+U- = R+U- + T+S-
Example: K2CO3(aq) + BaCl2(aq) 2KCl(aq) + BaCO3(s)
http://www.kentchemistry.com/links/Kinetics/DRFlash.htm
Combustion Reactions
An element or compound reacts with oxygen often producing energy as heat or light.
General Reaction: CxHy + (x + y/4) O2 xCO2 + (y/2)H2O
Example: CH4 (g) + 2O2 (g) CO2(g) + 2H2O (g)
Name each type of reaction
1) 2Mg(s) + O2(g) 2 MgO(s)
2) 2HgO(s) 2 Hg(l) + O2(g)
3) CH4 (g) + 2O2 (g) CO2(g) + 2H2O (g)
4) 2K(s) + 2H2O(l) 2KOH(aq) + H2(g)
5) K2CO3(aq) + BaCl2(aq) 2KCl(aq) + BaCO3(s)
Name each type of reaction 1) 2Mg(s) + O2(g) 2 MgO(s)
Combination
2) 2HgO(s) 2 Hg(l) + O2(g)
Decomposition
3) CH4 (g) + 2O2 (g) CO2(g) + 2H2O (g) Combustion
4) 2K(s) + 2H2O(l) 2KOH(aq) + H2(g)
Single Replacement
5) K2CO3(aq) + BaCl2(aq) 2KCl(aq) + BaCO3(s)
Double Replacement
Chapter 8.3 Reactions in Aqueous (aq) Solutions
Net Ionic Equations Predicting the Formation of a Precipitate
Net Ionic Equations
AgNO3(aq) + NaCl (aq) AgCl(s) + NaNO3 (aq) Double Replacement Reaction
Most ionic compounds dissociate (separate) into ions (cations and anions) when they dissolve in water.
When all ions dissociate, we write the equation with the charges on it. = Complete Ionic Equation
Complete Ionic Equation
Ag+(aq) + NO3
-(aq) + Na+
(aq) Cl-(aq) AgCl(s) + Na+(aq)
+ NO3-(aq)
The equation can be simplified by crossing out any ions that do not participate in the reaction. You do this by canceling out ions that appear on both sides.
Ag+(aq) + NO3
-(aq) + Na+
(aq) Cl-(aq) AgCl(s) + Na+(aq)
+ NO3-(aq)
You are left with the Net Ionic Equation: Ag+
(aq) + Cl-(aq) AgCl(s)
Pb(s) + AgNO3(aq) Ag(s) + Pb(NO3)2(aq)
Pb(s) + Ag+(aq)
+ NO3 -(aq) Ag(s) + Pb2+
(aq) + 2NO3-(aq)
Pb(s) + Ag+(aq)
Ag(s) + Pb2+(aq)
Need to balance charges
Pb(s) + 2Ag+(aq)
2Ag(s) + Pb2+(aq)
Predicting the Formation of a Precipitate
Table F in reference table
