Chemical Reactions
1 – Nature of Chemical Reactions
2 – Chemical Equations
3 - Reaction Types
4 – Reaction Rates and Equilibrium
State Standards
• CLE.3203.1.9 – Apply the Laws of Conservation of
Mass/Energy to balance chemical equations
• CLE.3202.Inq.4 – Apply qualitative and
quantitative measures to analyze data and draw
conclusions that are free of bias
• CLE.3202.Inq.6 – Communicate and defend
scientific findings
1 - Nature of Chemical Reactions
Key Questions :
• When do chemical reactions take place?
• What is the role of energy in chemical reactions?
Chemical Reactions
• Everyday occurrences are reactions ( rxns )
– Growing, ripen, decay, burn
• Chemical reactions stem from chemical changes
• How do you tell that a chemical change happens?
Chemical Reactions
• Atoms are rearranged ( to form new substance )
• Reactant – substance participating in rxn
• Product – substance being formed by rxn
Demonstration
• Add vinegar ( acetic acid ) to baking soda
• CO2 is produced
• What evidence of a reaction is obsered?
Energy & Chemical Reactions
• Energy factors into the state of matter
• Energy also plays a role in changes of state
• Chemical changes use energy also
• Same for chemical rxns
Chemical Reactions
• Involve changes in energy ALWAYS
• Energy is required to break bonds
• Forming bonds releases energy
Chemical Reactions
• Energy is conserved in rxns
• Exothermic – Rxns that release energy
• Endothermic – Rxns that absorb energy
Endothermic - Exothermic
Photosynthesis
• An endothermic rxn
1 - Nature of Chemical Reactions
Key Questions :
• When do chemical reactions take place?
• What is the role of energy in chemical reactions?
2 - Chemical Equations
Key Questions :
• What is a chemical equation?
• What can a balanced chemical equation tell you?
Describing Reactions
• Can write a word equation
• A chemical equation uses symbols to represent a
chemical reaction and shows the relationship
between the reactants and products
Conservation of Mass
• An equation must be balanced
• CH4 + O2  CO2 + H2O ( NOT BALANCED )
• CH4 + 2O2  CO2 + 2H2O ( BALANCED )
• Balance by adding coefficients so that there
are EQUAL NUMBERS OF EACH ELEMENT on
both sides of the “Yield” sign
Balanced Equations & Mole Ratios
• A balanced equation indicates the molar ratio
– This is the proportion of reactants and products
• Or relative amounts of a reactant to product
• CH4 + 2O2  CO2 + 2H2O
• Molar Ratio of methane to carbon dioxide?
• Molar ratio of methane to oxygen?
Molar Ratios can be shown as MASS
• How do we do this?
2 - Chemical Equations
Key Questions :
• What is a chemical equation?
• What can a balanced chemical equation tell you?
3 – Reaction Types
Key Questions :
• How does learning about reaction types help in
understanding chemical reactions?
• In which kinds of chemical reactions do the
numbers of electrons in atoms change?
Classifying Reactions
• Can use patterns to identify kinds of chemical
reactions and to predict the products of the
chemical reactions
• For example : small molecules join to form a
larger one by a certain type of reaction
Synthesis Reactions
• Synthesis reactions occur when multiple
substances combine to form a new compound
• General form : A + B  AB
• Single compound formed
• Example : plastic ( polymers – remember GOOP? )
Decomposition Reactions
• Decomposition occurs when substances are
broken apart ( Opposite of Synthesis )
• Cracking – large molecules of C and H
(hydrocarbons) are broken apart
• Digestion – similar to cracking
• General form : AB  A + B
Combustion Reactions
• CH4 + 2O2  CO2 + 2H2O ( methane combustion )
• When oxygen reacts with a substance ( burning )
• Usually an organic material
– Hydrocarbon
– Plant matter ( wood ) or clothing ( cotton/polymeric )
• Not always though – ammonia ( NH3 )
3
4
– NH3 + O2  NO2 +
3
HO
2 2
Displacement Reactions
• Single displacement rxn occurs when one atom
appears to take the place of another
• General form : AX + B  BX + A
• Double displacement rxn occurs when two
compounds appear to exchange ions
• General form : AX + BY  BX + AY
Electrons & Chemical Reactions
• Free radical reactions and redox reactions can be
understood as changes in the numbers of
electrons that atoms have
• Free radical is an atom or a group of atoms that
has one unpaired electron
• Redox reactions ( oxidation-reduction ) occur
when one substance loses electrons and another
substance gains electrons
3 – Reaction Types
Key Questions :
• How does learning about reaction types help in
understanding chemical reactions?
• In which kinds of chemical reactions do the
numbers of electrons in atoms change?
4 – Reaction Rates & Equilibrium
Key Questions :
• What speeds up a reaction?
• What does a catalyst do?
• What happens when a reaction goes both directions
What is Reaction Rate?
• How fast a reaction
proceeds
• Can explain by finding
the amount of products
produced in a certain
time interval
What Speeds up Reactions?
• Higher temperatures
• More surface area
• Higher reactant
concentration
– ( amount / vol )
• Pressure / Size of
compound or molecule
What is a catalyst?
• Speeds up or slows down a reaction but is not
altered by the reaction
• It does not participate as a reactant or a
product
• In your body – ENZYMES are catalysts
Equilibrium
• Like balance when you are walking
• Balance between products and reactants
when a reaction goes forward and backwards
4 – Reaction Rates & Equilibrium
Key Questions :
• What speeds up a reaction?
• What does a catalyst do?
• What happens when a reaction goes both directions