CHEM Chapter 7- Classifying Chemical Reactions
CHEM Chapter 7- Classifying Chemical Reactions Chem 1301
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This 5 page Class Notes was uploaded by Kayra Reyes on Wednesday September 28, 2016. The Class Notes belongs to Chem 1301 at University of Houston taught by Roman S. Czernuszewicz in Fall 2015. Since its upload, it has received 11 views. For similar materials see Foundations of Chemistry in Chemistry at University of Houston.
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Date Created: 09/28/16
th th Chapter 7 from “Introductory Chemistry” by Zumdahl and Decoste, 7 /8 edition *Majority of the chemical reactions that take place in our bodies occur in aqueous solutions Ex: oxygen dissolving into blood stream Pg 137. PREDICTING IF A REACTION WILL HAPPEN Driving Force: “changes that make reactions go in the direction of the arrow,” the cause of the product Most common driving forces: 1. Forms a solid 2. Forms of water 3. Transfers electrons 4. Forms a gas -if two or more chemicals are joined together and any of these happened, there most likely is a chemical reaction REACTION: SOLID FORMS Precipitation: process by which a solid is formed Precipitate: the solid formed Precipitation Reaction: the reaction itself Ionic Compounds in Aqueous Solutions *In majority of “solid containing ions dissolved in water, the ions separate and move around independently” -if electricity is conducted, then there are separated ions in the chemical (ex: pure water does not have separate ions, therefore, pure water does not conduct electricity) Strong Electrolyte: substance of which each unit in an aqueous solutions produces separate ions (Ex: Barium Nitrate= Ba(NO ) , s3 2rates into ions: Ba , NO , NO ) 3 3- In a mixed solution, though the equation can be written as Formula + Formula Products, it’s more appropriate to write it as Formula separated into ions + Formula separated into ions Products Ex: K2CrO 4aq) + Ba(NO ) (3 2 Products Vs. 2K (aq) + CrO (a4) + Ba (aq) + 2NO (aq) 3roducts Pg 139. FINDING WHAT IS FORMED IN A PRODUCT Figuring out what the product of a reaction will form is very difficult, so in order to do so, you must first consider all the possible products based on the reactants provided *Solids must have a zero net charge, so it can only be formed by a negative plus positive charged ion, aka a cation and an anion Ex: K and Ba both positive= not a solid OR CrO 42-and NO b3th negative= not a solid -However, chemists have found that most ionic compounds contain two types of ions + - + - Ex: NaCl Na and Cl OR KOH K and OH Pg 141. SOLUBILITY RULES To identify a product one needs two types of chemical knowledge: 1. Knowledge of facts *make sure you memorize key facts like the reactions between common chemicals and the charges of formulas 2. Knowledge of concepts *make sure you understand crucial concepts like the fact that, solids are an anion plus a cation or that an electric current means ions are separate in a solution *Note: positively charged ions DON’T ALWAYS make a solid Ex: NaCl (aka salt), when placed in water does not form a solid, instead salt dissolves Soluble Solid: solid that readily dissolves in water Insoluble Solid: solid for which such a tiny amount dissolves that there is no noticeable change in physical state, can’t see it dissolve Pg 142. IDENTIFYING PRECIPITATIONS IN REACTIONS WHERE SOLIDS FORM Ion Interchange: trading cations and anions between separate formulas, taking the cation in one formula and putting it with the anion of the other formula *Memorize General Rules for Solubility of Ionic Compounds (salts) in Water: 1. Most Nitrate salts are soluble (NO ) 3 2. Most salts of Na , K , and NH ar4 soluble 3. Most chloride salts are soluble. (except: AgCl, PbCl , a2d Hg Cl )2 2 4. Most sulfate salts are soluble. (except: BaSO , P4SO , an4 CaSO ) 4 5. Most hydroxide (OH) compounds are only slightly soluble. (except: NaOH and KOH *Ba(OH) an2 Ca(OH) are o2ly moderately soluble) 6. Most sulfide (S 2, carbonate (CO ), 3nd phosphate (PO ) salts a4e only slightly soluble Pg 145. PREDICTING THE PRECIPITATE OF TWO MIXED IONIC COMPOUNDS Step 1: Write the reactants as they actually exist before any reaction occurs. Remember that when a salt dissolves, its ions separate. Step 2: Consider various solids that could form. Exchange the ions of the added salts. Step 3: Use the solubility rules to decide whether a solid forms and, if so, to predicts the identity of the solid Pg 147. DESCRIBING REACTIONS IN AQUEOUS SOLUTIONS Molecular Equation: shows complete formulas in reactions but doesn’t give clear details as to what happens in the solution Complete Ionic Equation: “better represents the actual forms of the reactants and products in solution. In a complete ionic equation, all substances that are strong electrolytes are represented as ions” Spectator Ions: ions that do not directly participate in a reaction Net Ionic Equation: includes only elements and formulas that are directly involved in the reaction Pg 148. TYPES OF EQUATIONS FOR REACTIONS IN AQUEOUS SOLUTIONS Molecular Equation Ex: Pb(NO ) 3 2) + Na SO (2q) 4 PbSO (s) + 2Na4O (aq) 3 Complete Ionic Equation Ex: Pb (aq) + 2NO (aq)3+ 2Na (aq) + SO 42-(aq) PbSO (s)4+ 2Na + (aq) + 2NO (aq) 3- *PbSO4 is a solid so it’s not separated, all ions are separated Net Ionic Equation 2+ 2- Ex: Pb (aq) + SO 4 (aq) PbSO (s4 *Na and NO3 don’t undergo chemical change, thus they are not included, PbSO is a soli4 so it’s not separated Pg 149. REACTIONS THAT FORM WATER: ACIDS AND BASES + Acids: Substance that produces H ions (protons) when dissolved in water *known for sour taste Strong Acid: gives large amount of H ions when dissolved in water, strong electrolytes Bases: Substance that produces Hydroxide ions (OH ) in water *known for bitter taste and slippery feel Strong Base: gives large amount of OH ions when dissolved in water, strong electrolytes -H ions react with OH ions to make water H O 2 Pg 151. Ex: Molecular Equation HNO (3q) + KOH (aq) H O (l) 2 KNO (aq) 3 Complete Ionic Equation + - + - + - H (aq) + NO (a3) + K (aq) + OH (aq) H O (l) + K2(aq) + NO (aq) 3 Net Ionic Equation H (aq) + OH (aq) H O (l)2 Salts: ionic compounds formed Pg 152. KEY POINTS ON STRONG ACIDS AND BASES - Common strong acids are (aq) solutions of HCl, HNO , and H3SO 2 4 - Strong acid is a substance that completely (ionizes) separates into ions in water - “Strong base is a metal hydroxide compound that is very soluble in water” Most common strong bases are NaOH and KOH - The net ionic equation for the reaction of a strong base and acid is ALWAYS H (aq) + OH (aq) H O (l) 2 - In the reaction of a strong base and acid, one product is ALWAYS water and the other is ALWAYS salt, which remain dissolved in water, only able to be separated once the water is evaporated - “The reaction of H+ and OH- is often called an acid-base reaction, where the H+ is the acidic ion and the OH- is the basic ion” Pg 153. REACTIONS OF METALS WITH NON-METALS OXIDATION REDUCTION -reaction involves the transfer of one or more electrons from the metal (cation) to the non- metal (anion) Oxidation-Reduction Reaction Characteristics of Oxidation-Reduction Reaction: 1. Metal + non-metal = ionic compound, electron transfer makes the metal a cation and the non-metal an anion 2. Two non-metals can also undergo oxidation-reduction reactions in which O2 is in the reactants and products, however, two non-metals AREN’T ionic Pg 156. WAYS TO CLASSIFY REACTIONS Precipitation Reaction: two solutions mixed together to form a solid Double-Displacement Reaction: when two anions are exchanged in the products AB + CD AD + BC Acid-Base Reaction: a strong acid and strong base mix to form water Oxidation-Reduction Reaction Single-Replacement Reaction: like double-displacement reaction except only one anion is moved A + BC B+AC Forming of a gas Ex: Zn (s) + 2HCl (aq) H (2) + ZnCl (2q) Pg 159. OTHER REACTION CLASSIFICATIONS Combustion Reaction: chemical reaction in which the oxygen produced creates energy as heat so quickly it forms a flame *these are a type of oxidation-reduction reaction *most combustion reactions are used to make heat or electricity for homes Synthesis (Combination) Reactions: compound formed from simpler materials Examples of synthetic compounds: plastic, polyester, and aspirin Ex: synthesis of carbon dioxide: C(s) + O2 (g) CO2 (g) Decomposition Reaction: compounds broken down into simpler compounds or elements, usually done by applying heat or electric current Ex: 2H2O (l) electric current 2H (2) + O (2)
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