Reaction Type Notes

 Most chemical reactions can be categorized into one of five types.  You can usually identify the reaction type by looking at the reactants. Once the type of reaction is identified, we can predict the products.

Reaction Type Notes Chemists classify reactions in order to organize the many types: A synthesis reaction is a reaction in which two or more substances react to produce a single product. General form: A + B  AB or A + BC  ABC or AB + CD  ABCD

Types of Chemical Reactions When two elements react, the reaction is always a synthesis reaction.

Reaction Type Notes Example: 2 H 2 + O 2  2 H 2 O

Reaction Type Notes Synthesis:  To predict the products: for binary compounds, put elements together and balance the total charges. Otherwise, just combine.  These reactions generally happen spontaneously, and are generally exothermic (release energy).

Types of Chemical Reactions In a combustion reaction, oxygen combines with another substance and releases energy in the form of heat and light. Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.

Reaction Type Notes  Hydrocarbon combustion—a specific case of combustion in which a hydrocarbon (a substance only containing carbon and hydrogen) reacts with oxygen to form carbon dioxide and water  General form: C x H y + O 2  CO 2 + H 2 O

Reaction Type Notes Example: 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 O

Reaction Type Notes Hydrocarbon Combustion:  To predict products:  At least carbon dioxide and water. Always exothermic, but often requires a large activation energy, keeping it from happening spontaneously.

Decomposition Reactions A decomposition reaction is one in w hich a single compound breaks down into two or more elements or new compounds. Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur and be maintained. General form: AB  A + B

Reaction Type Notes Example: 2H 2 O 2  2 H 2 O + O 2 (Needs a catalyst—Potassium Iodide)

Reaction Type Notes Decomposition: To predict the products:  Binary compounds separate into their two elements.  You will be given a handout to predict others.  Generally not spontaneous, and generally endothermic.

Replacement Reactions A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction. General form: A + BX → AX + B

Replacement Reactions (cont.) A metal will not always replace a metal in a compound dissolved in water because of differing reactivities. An activity series can be used to predict if reactions will occur.

Replacement Reactions (cont.) Anions can replace anions in compounds. Halogens frequently replace other halogens in replacement reactions. Halogens also have different reactivities, like metallic elements. There is a separate activity series for anions.

Reaction Type Notes Example: 2 Na + 2 H(OH)  2 Na(OH)+ H 2

Reaction Type Notes Single displacement:  To predict the products: The element switches places with the element of similar charge within the compound.  If the element is more reactive, then the one it attempts to replace, then the reaction will be spontaneous and exothermic. Otherwise, it will not be spontaneous and will be endothermic (require the input of energy).

Activity Series: Most Active Cations  Least Active  Lithium  Rubidium  Potassium  Barium  Calcium  Sodium  Magnesium  Aluminum  Manganese  Zinc  Chromium  Iron  Nickel  Tin  Lead  Hydrogen  Copper  Mercury  Silver  Platinum  Gold *Red not included in book values Reaction Type Notes

Activity Series: Most Active Anions  Least Active  Fluorine  Oxygen  Chlorine  Nitrogen  Bromine  Iodine  Sulfur  Selenium  Astatine  Phosphorus  Tellurium  Arsenic  Polonium *Red not included in book values Reaction Type Notes

Double replacement reactions occur when ions are exchanged between two compounds. This figure shows the form of a double replacement equation.

Reaction Type Notes Double displacement: To predict the products:  Like charged particles switch places  Both compounds are initially stable and so reactions will usually not be spontaneous as solids. If compounds can be dissolved and dissociated (broken apart) then the reaction will usually occur spontaneously to some degree, but not be highly exothermic.

Example: 2 NaI(aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2NaNO 3 (aq) A solid product produced during a chemical reaction in a solution is called a precipitate. All double replacement reactions produce either water, a precipitate, or a gas. Reaction Type Notes

This table shows the steps to write double replacement reactions. Reaction Type Notes

 Most reactions which do not appear to fit any of these five patterns are usually a combination of two or more of them happening simultaneously.

Reaction Type Notes Practice Problem ANSWERS (page 291): Al(s) + 3 S(s)  Al 2 S 3 ; synthesis 15. H 2 O(l) + N 2 O 5 (g)  2HNO 3 (aq); synthesis NO 2 (g) + O 2 (g)  2N 2 O 5 (g); synthesis and combustion 17. H 2 SO 4 (aq) + 2NAOH(aq)  Na 2 SO 4 (aq) + 2H 2 O(l); synthesis

Reaction Type Notes Practice Problem ANSWERS (page 292): 18. 2Al 2 O 3 (s)  4 Al(s) + 3O 2 (g) 19. Ni(OH) 2 (s)  NiO(s) + 2H 2 O(l) NaHCO 3 (s)  Na 2 CO 3 (aq) + CO 2 (g) + H 2 O(l)

Reaction Type Notes Textbook Practice (page 295):  Problems #21-#24.  Answer in your lab composition journal.

Reaction Type Notes Textbook Practice ANSWERS: 21. 2K(s) + ZnCl 2 (aq)  Zn(s) + 2KCl(aq) 22. No Reaction—Cl is below F in the activity series 23. No Reaction—Fe is below Na in the activity series 24.2Al(s) + 3Pb(NO 3 ) 2 (s)  3Pb(s) + 2Al(NO 3 ) 3 (aq)

Reaction Type Notes Textbook Practice (page 297):  Problems #25-#27.  Answer in your lab composition journal.

Reaction Type Notes Textbook Practice ANSWERS: 25. LiI(aq) + AgNO 3 (aq)  AgI(s) + LiNO 3 (aq) 26. BaCl 2 (aq) + K 2 CO 3 (aq)  BaCO 3 (s) + 2KCl(aq) 27. Na 2 C 2 O 4 (aq) + Pb(NO 3 ) 2 (aq)  PbC 2 O 4 (s) + 2NaNO 3 (aq)

Replacement Reactions (cont.) This table summarizes different ways to predict the products of a chemical reaction.

Reaction Type Notes The following equation is what type of reaction? KCN(aq) + HBr(aq) → KBr(aq) + HCN(g) A.deconstructive B.synthesis C.single replacement D.double replacement

Reaction Type Notes Which of the following is NOT one of the four types of reactions? A.deconstructive B.synthesis C.single replacement D.double replacement