Chapter 11Chemical Reactions
Note Taking Tips!
• Paraphrase, paraphrase, paraphrase!
• Use symbols, arrows, pictures, and abbreviations whenever possible.
• Write side notes to help you remember concepts.
What is a chemical reaction?– Occur every minute of every day!– When one or more reactants change into one
or more products. – Characterized by the breaking of bonds in
reactants and formation of bonds in products
Law of Conservation of Mass
• In any physical or chemical reaction, mass is conserved; mass can be neither created nor destroyed
Chemical Reactions
• Chemical reactions are described by chemical equations. • Skeleton Equation: chem equation that doesn’t indicate relative
amounts of reactants and products.
Fe + O2 Fe2O3
Reactants Products
It needs to be balanced!!!
Draw this one
It means the reaction is reversible
• Catalyst: a substance that speeds up the reaction but is not used up in a reaction. – Neither a reactant nor a product– Written above arrow in chem equation.
MnO2
H2O2(aq) H20(l) + O2(g)
Balancing Act
• Bicycle scenario
Balancing Chemical Equations
• A chemical reaction where each side of the equation has the same number of atoms of each element and mass is conserved.
Fe + O2 > Fe2O3
Steps to Balancing1. Count atoms on each side. Count polyatomic ion as one unit
if it appears unchanged on right.
2. Balance elements one at a time using coefficients– Balance elements that appear only once 1st
– Never change subscripts
3. Check work and make sure all coefficients are in lowest possible ratio.
H2 + O2 > H2O
Let’s try some!
Let’s try some!
1. _____ S + _____ O2 --> _____ SO2
2. _____ Na + _____ O2 --> _____ Na2O2
3. _____ Hg + _____ O2 --> _____ HgO
4. _____ Ag2O --> _____ Ag + _____ O2
Let’s try some!
Practice
Practice
11.2 Types of Chemical Reactions
Concept map
•5 general types– Combination– Decomposition– Single-replacement– Double-replacement– Combustion
Concept map instructions
• Get basic definition
• Write at least one chemical reaction
• Describe the demonstration reaction
Combination
• When 2 or more substances react to form a single new substance.
2Mg + O2 > 2MgO
Decomposition
• When a single compound breaks down into 2 or more simpler products.
• 1 reactant, 2 or more products• Usually require heat, light, or electricity to occur.
2HgO > 2Hg + O2
Single-Replacement
• When 1 element replaces a second element in a compound.
2K + 2H2O > 2KOH + H2
Look at the switch!
Double-Replacement
• An exchange of positive ions between 2 compounds.
• Usually produces one of the following– A precipitate– A gas– water
• Remember: positive ions=cations=on left side of a compound
• Na2S + Cd(NO3)2 > CdS + 2NaNO3• 2NaCN + H2SO4 > 2HCN + Na2SO4• Ca(OH)2 + 2HCl > CaCl2 + 2H2O
Combustion• When an element or compound reacts with oxygen, it produces
energy in the form of heat and light. • Oxygen is always a reactant• The other reactant is often a hydrocarbon (something with hydrogen
and carbon)– CH4 methane– C3H8 propane– C4H10 butane– C8H18 gasoline
• CO or CO2 can also be products
2C8H18 + 25O2 > 16CO2 + 18H2O
Practice!
Your Task
• Dissecting a chemical reaction
