Chemical Reactions: Prediction & Classification

1. Predicting Products of Chemical Reactions

2. Objectives • Predict the products of synthesis, decomposition, single replacement, double replacement, and combustion reactions. • List three types of products that drive double replacement reactions.

3. Initial Questions • Why classify reactions? • How many basic classes of reactions are there? • List the basic classes of reactions? • What is the basis for each class of reactions.

4. Combustion Reactions • Combustion Reactions: • The products of the combustion of a hydrocarbon are always carbon dioxide and water vapor.

5. Combustion Reactions • Example 1: • C6H6 + O2 --> • Example 2: • C2H5OH + O2 -->

6. Combustion Reactions • Example 1: • 2 C6H6 + 15 O2 --> 12CO2 + 6 H2O • Example 2: • 1 C2H5OH + 3 O2 --> 2 CO2 + 3 H2O

7. Synthesis Reactions • Synthesis Reactions: • Since a synthesis reaction is one where two or more elements (or simple compounds) combine to form a single compound, the resulting product must contain all elements/ions present in the reactants without any leftover or additional elements/ions. The product is a single product with balanced charges and the equation must be able to be balanced with correct coefficients.

8. Synthesis Reactions • Example 3: phosphorus + oxygen --> diphosphorus pentoxide • (Recall oxygen is diatomic.) • Example 4: sodium + chlorine -->

9. Synthesis Reactions • Example 3: phosphorus + oxygen --> diphosphorus pentoxide • (Recall oxygen is diatomic.) • 4 P + 5 O2 --> 2 P2O5 • Example 4: sodium + chlorine --> • 2 Na + Cl2 --> 2 NaCl

10. Decomposition Reactions • Decomposition Reactions: • Since a decomposition reaction is one where a single reactant breaks into two or more elements (or simple compounds), the resulting products must contain all elements/ions present in the reactant with no leftover. The rules are the same for a synthesis – since they are opposite reactants.

11. Decomposition Reactions • Example 5: copper (I) chloride --> • (Recall chlorine is diatomic.) • Example 6: water -->

12. Decomposition Reactions • Example 5: copper (I) chloride --> • (Recall chlorine is diatomic.) • 2 CuCl --> 2 Cu + Cl2 • Example 6: water --> • 2 H2O --> 2 H2 + O2

13. Single Replacement Reactions • Single Replacement Reactions: • In a single replacement reaction, either the positive or negative ion of one reactant is replaced by the other reactant (an element that forms either a positive or negative ion). Only positive ions may replace other positive ions and only negative ions may replace other negative ions.

14. Single Replacement Reactions • Example 7:aluminum + barium chloride --> • Example 8: ammonium oxide + iodine -->

15. Single Replacement Reactions • Example 7:aluminum + barium chloride --> • 2 Al + 3 BaCl2 --> 3 Ba + 2 AlCl3 • Example 8: ammonium oxide + iodine --> • 2 (NH4)2O + 2 I2 --> 4 NH4I + O2

16. Double Displacement Reactions • Double Replacement Reactions (Metathesis Reactions): • In a double replacement reaction, each reactant ion gets a new partner; the positive ions switch thereby giving everyone a new partner. There are two reactants, each compound is made of two ions (one positive and one negative). When positive ions switch, each positive ion must end up with a negative ion (not one to which it had been previously attached). The compounds are written so there is a zero net charge and then the equation is balanced.

17. Double Displacement Reactions • Ex 9: sodium chloride + aluminum oxide --> • Ex 10:potassium permanganate + calcium phosphate

18. Double Displacement Reactions • Ex 9: sodium chloride + aluminum oxide --> • 6 NaCl + Al2O3 --> 3 Na2O + 2 AlCl3 • Ex 10:potassium permanganate + calcium phosphate • 6 KMnO4 + Ca3(PO4)2 --> 2 K3PO4 + 3Ca(MnO4)2

19. Final Questions • What three things drive the products of a double displacement reaction? • What is true of a combustion reaction? • What is true of synthesis and decomposition reactions?

20. HOT STUFF

21. TAKS Objective 3 – The student will demonstrate an understanding of the structures and properties of matter. • Complex interactions occur between matter and energy.

22. TEKS 8.10 (C) The student knows that complex interactions occur between matter and energy. The student is expected to: identify and demonstrate that loss or gain of heat energy occurs during exothermic and endothermic chemical reactions.

23. Learning Objectives • identify endothermic and exothermic reactions associated with chemical changes • Explain the loss or gain of heat during chemical reactions • Identify chemical and physical changes associated with endothermic and exothermic reactions

24. Background Heat- transfer of energy

25. Exothermic- heat energy EXITS the system - ex. Combustion, evaporation of water - surroundings usually feel warmer

26. Salt An example of an exothermic reaction is the mixture of sodium metal and chlorine gas which yields table salt. 2Na(s) + Cl2(g)  2NaCl(s) + energy

27. Endothermic- heat energy ENTERS the system - ex. Cold packs, melting ice - surroundings usually feel cooler

28. How do cold packs work? The outer pouch contains water. The inner pouch contains ammonium-nitrate. When you “pop” the inner pouch, the chemical reaction absorbs heat energy from the surroundings. This is an endothermic reaction. The temperature of the solution falls to about 35 F for 10 to 15 minutes.

29. Photosynthesis During photosynthesis, plants absorb the energy from the sun to convert carbon dioxide and water into glucose and oxygen. sunlight + 6CO2(g) + 6H2O(l)  C6H12O6(aq) + 6O2(g)

30. Physical change- change in size, shape or state of matter

31. Chemical Reaction - process in which one or more substances are changed into others. Chemical reactions are accompanied by a loss or gain of energy.

32. True or False Chemical reactions always produce heat

33. Chemical reactions can release or absorb heat, but can also create light, sound or electricity!

34. True or False Heat can be lost, destroyed or just disappear

35. Heat energy is transferred from one object to another, or is transferred to another form of energy, but never disappears. Law of Conservation of Energy

36. True or False Color change is always a physical property

37. Color is a physical property. Color change can be the result of a chemical change.

38. ENGAGE • Cold Packs • Rubber Bands • Glo-sticks

39. EXPLORE • Hot or Not • students explore endothermic and exothermic chemical reactions using baking soda and calcium chloride

40. EXPLAIN • List 3 physical properties of matter. • List 3 physical properties for: • Calcium chloride • Baking soda • Phenol red solution

41. Describe what happens with baking soda and calcium chloride are mixed. • Describe what happens with baking soda, calcium chloride and phenol red are mixed. • What are evidences of chemical change?

42. Is this an endothermic or exothermic reaction? How do you know? • Give three examples of exothermic reactions in everyday life.

43. ELABORATE • Ice Ice Baby • Baking soda and vinegar • Is this endothermic or exothermic? How do you know? • Give 3 examples of everyday endothermic reactions.

44. Ice Cream • Are the changes physical or chemical? • Is the ice cream endothermic or exothermic? How do you know? • Is the ice/salt mix endothermic or exothermic? How do you know?

45. EVALUATION • Complete Type of Change? Endo/Exo chart • Complete graph analysis questions