Chemical Reactions Unit 1: Chemistry Basics 1.32 Chemical Reactions Textbook ch 3.2

Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons. Students will be able to demonstrate understanding by laboratory investigation, analysis of data and creation of models. SWBAT: LO 1.18 The student is able to apply conservation of atoms to the rearrangement of atoms in various processes. LO 3.1 Students can translate among macroscopic observations of change, chemical equations, and particle views. LO 3.2 The student can translate an observed chemical change into a balanced chemical equation and justify the choice of equation type (molecular, ionic, or net ionic) in terms of utility for the given circumstances. LO 3.5 The student is able to design a plan in order to collect data on the synthesis or decomposition of a compound to confirm the conservation of matter and the law of definite proportions. LO 3.6 The student is able to use data from synthesis or decomposition of a compound to confirm the conservation of matter and the law of definite proportions. AP Learning Objectives :

Types of Reactions There are five types of chemical reactions we will talk about: Synthesis (or combination) reactions Decomposition reactions Combustion reactions Single replacement (or displacement ) reactions Double replacement (or displacement ) reactions (including Acid base neutralization) You need to be able to identify the type of reaction and predict the product(s)

Steps to Writing Reactions Some steps for doing reactions Identify the type of reaction Predict the product(s) using the type of reaction as a model Balance it Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O 2 as an element. In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

1. Synthesis reactions Synthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.) reactant + reactant  1 product Hint: You can tell its synthesis b/c only 1 product Basically: A + B  AB Example: 2H 2 + O 2  2H 2 O Example: C + O 2  CO 2

Synthesis (or combination) Reactions Here is another example of a synthesis reaction

Practice Predict the products. Write and balance the following synthesis reaction equations. Sodium metal reacts with chlorine gas Na (s) + Cl 2(g)  Solid Magnesium reacts with fluorine gas Mg (s) + F 2(g)  Aluminum metal reacts with fluorine gas Al (s) + F 2(g) 

2. Decomposition Reactions Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds 1 Reactant  Product + Product Hint: You can tell its synthesis b/c only 1 reactant In general: AB  A + B Example: 2 H 2 O  2H 2 + O 2 Example: 2 HgO  2Hg + O 2

Decomposition Reactions

Decomposition Exceptions!!!!! Carbonates and chlorates are special case decomposition reactions that do not go to the elements. Carbonates (CO 3 2- ) decompose to carbon dioxide and a metal oxide Example: CaCO 3  CO 2 + CaO Chlorates (ClO 3 - ) decompose to oxygen gas and a metal chloride Example: 2 Al(ClO 3 ) 3  2 AlCl O 2

Practice Predict the products. Then, write and balance the following decomposition reaction equations: Solid Lead (IV) oxide decomposes PbO 2(s)  Aluminum nitride decomposes AlN (s)  Sodium carbonate decomposes Na 2 CO 3 

3. Combustion Reactions Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)

Combustion Reactions In general: C x H y + O 2  CO 2 + H 2 O Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C 8 H 18 ) Example C 5 H O 2  5CO 2 + 6H 2 O

4. Single Replacement Reactions Single Replacement Reactions occur when one element replaces another in a compound. A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). element + compound  element + compound A + BC  AC + B (if A is a metal) OR A + BC  BA + C (if A is a nonmetal) (remember the cation always goes first!) When H 2 O splits into ions, it splits into H + and OH - (not H+ and O -2 !!)

Single Replacement Reactions

Write and balance the following single replacement reaction equation: Zinc metal reacts with aqueous hydrochloric acid Zn (s) + HCl (aq)  ZnCl 2 + H 2(g) Note: Zinc replaces the hydrogen ion in the reaction Sodium chloride solid reacts with fluorine gas NaCl (s) + F 2(g)  NaF (s) + Cl 2(g) Note that fluorine replaces chlorine in the compound 2

5. Double Replacement Reactions Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound Compound + compound  compound+ compound AB + CD  AD + CB

Double Replacement Reactions Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together Example: AgNO 3(aq) + NaCl (s)  AgCl (s) + NaNO 3(aq) Another example: K 2 SO 4(aq) + Ba(NO 3 ) 2(aq)  KNO 3(aq) + BaSO 4(s) 2

Practice Predict the products. Balance the equation HCl (aq) + AgNO 3(aq)  CaCl 2(aq) + Na 3 PO 4(aq)  Pb(NO 3 ) 2(aq) + BaCl 2(aq) 

Gas-Forming Reactions More exceptions! More exceptions! These reactions do not give the product expected. These Double Replacement reactions do not give the product expected. The expected product decomposes to give a gaseous product (CO 2 or SO 2 ). The expected product decomposes to give a gaseous product (CO 2 or SO 2 ). CaCO 3 (s) + HCl (aq)  CaCl 2 (aq) + CO 2 (g) + H 2 O (l) NaHCO 3 (aq) + HBr (aq)  NaBr (aq) + CO 2 (g) + H 2 O (l) SrSO 3 (s) + 2 HI (aq)  SrI 2 (aq) + SO 2 (g) + H 2 O (l)

Gas-Forming Reactions This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! Just as in the previous examples, a gas is formed as a product of this reaction: Just as in the previous examples, a gas is formed as a product of this reaction: Na 2 S (aq) + H 2 SO 4 (aq)  Na 2 SO 4 (aq) + H 2 S (g)

Summary of gas rxns H 2 S is a gas H 2 S is a gas If you produce: H 2 CO 3 then it breaks down to H 2 O + CO 2(g) H 2 CO 3 then it breaks down to H 2 O + CO 2(g) H 2 SO 3 then it breaks down to H 2 O + SO 2(g) H 2 SO 3 then it breaks down to H 2 O + SO 2(g) NH 4 OH then it breaks down to H 2 O + NH 3(g) NH 4 OH then it breaks down to H 2 O + NH 3(g)

References I modified the original to fit our needs in AP Chemistry needs. Our textbook: Brown, Lemay et all. AP edition chemistry, 13 th edition,