1 – Nature of Chemical Reactions 4 – Reaction Rates and Equilibrium 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 ) NH3 + 3 4 O2  NO2 + 3 2 H2O

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