Chemical Reactions

1. Chemical Reactions 1 – Nature of Chemical Reactions 2 – Chemical Equations 3 - Reaction Types 4 – Reaction Rates and Equilibrium

2. 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

3. 1 - Nature of Chemical Reactions Key Questions : • When do chemical reactions take place? • What is the role of energy in chemical reactions?

4. 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?

5. Chemical Reactions • Atoms are rearranged ( to form new substance ) • Reactant – substance participating in rxn • Product – substance being formed by rxn

6. Demonstration • Add vinegar ( acetic acid ) to baking soda • CO2 is produced • What evidence of a reaction is obsered?

7. 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

8. Chemical Reactions • Involve changes in energy ALWAYS • Energy is required to break bonds • Forming bonds releases energy

9. Chemical Reactions • Energy is conserved in rxns • Exothermic – Rxns that release energy • Endothermic – Rxns that absorb energy

10. Endothermic - Exothermic

11. Photosynthesis • An endothermic rxn

12. 1 - Nature of Chemical Reactions Key Questions : • When do chemical reactions take place? • What is the role of energy in chemical reactions?

13. 2 - Chemical Equations Key Questions : • What is a chemical equation? • What can a balanced chemical equation tell you?

14. 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

15. 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

16. 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?

17. Molar Ratios can be shown as MASS • How do we do this?

18. 2 - Chemical Equations Key Questions : • What is a chemical equation? • What can a balanced chemical equation tell you?

19. 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?

20. 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

21. 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? )

22. 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

23. 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 + O2  NO2+ H2O

24. 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

25. 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

26. 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?

27. 4 – Reaction Rates & Equilibrium Key Questions : • What speeds up a reaction? • What does a catalyst do? • What happens when a reaction goes both directions

28. What is Reaction Rate? • How fast a reaction proceeds • Can explain by finding the amount of products produced in a certain time interval

29. What Speeds up Reactions? • Higher temperatures • More surface area • Higher reactant concentration • ( amount / vol ) • Pressure / Size of compound or molecule

30. 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

31. Equilibrium • Like balance when you are walking • Balance between products and reactants when a reaction goes forward and backwards

32. 4 – Reaction Rates & Equilibrium Key Questions : • What speeds up a reaction? • What does a catalyst do? • What happens when a reaction goes both directions