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Predicting Products of Chemical Reactions Honors Chemistry Ch 10 (Still)
Identify the type of reaction. This is key to predicting products. The type of reaction will be a guide to the products that will form in the chemical reaction. The reason is the products for each type of reaction follow a pattern. After you predict the products don’t forget to make sure the equation is balanced.
Synthesis Reactions Remember the general equation? General Equation A + B AB We can predict the products if the reactants are two elements. (Look at how they would form ionic or covalent compounds)
Examples: Mg + N 2 Ca + Cl 2 Al + O 2 Mg 3 N 2 CaCl 2 Al 2 O 3 3 342
Decomposition Reactions General Equation AB A + B You can predict the products if it is a binary compound Made up of only two elements The reactant compound breaks apart into its elements
Combustion Reactions There are a lot of different combustion reactions The important things to remember are: Oxygen will always be one of the reactants A release of energy in the form of light and heat will occur When oxygen reacts with hydrocarbons usually carbon dioxide and water (along with light and heat) will be the products
Examples: Mg (s) + O 2 C 2 H 6 (g) + O 2 MgO22 CO 2 + H 2 O6472
Single-replacement Reactions General Equation: A + BX AX + B General Equation: A + BX AX + B Use the activity series (for metals) or periodic table (for nonmetals) to see if the reaction can occur. Use the activity series (for metals) or periodic table (for nonmetals) to see if the reaction can occur.
More examples: K + Mg(OH) 2 Zn + HCl Br 2 + HCl
Double-replacement Reactions General Equation: AX + BY AY + BX General Equation: AX + BY AY + BX The ions change places to form two new compounds. The ions change places to form two new compounds. One of the products will usually be either: One of the products will usually be either: - a precipitate (solid) - a gas that bubbles out. - a covalent compound (usually water). You will need to use the solubility rules to see if the reaction will occur. You will need to use the solubility rules to see if the reaction will occur.
Neutralization Reactions General Equation: General Equation: Acid (aq) + Base (aq) Salt (aq) + Water (l) Generally the salt is an ionic compound made up of a cation from a base and an anion from an acid. The water is formed from the H from the acid and the OH from the base.
Practice Examples: Nitric acid and cesium hydroxide HBr (aq) + Ca(OH) 2 (aq)
More Practice Examples: sulfuric acid + potassium hydroxide H 2 CO 3 (aq) + NH 4 OH (aq)
Reactions in Aqueous Solutions Many reactions occur when substances are dissolved in water. In aqueous solutions water is the solvent The compounds dissolved in water are the solute.
Aqueous solutions of molecular compounds Some solutions have molecular compounds as the solute. Ex: sugar (C 6 H 12 O 6 ) and ethanol (C 2 H 5 OH) These substances dissolve in water but do not break apart. They do not undergo a chemical change. Other substances, like some ionic compounds do undergo a chemical change when they dissolve.
Aqueous solutions of Ionic Compounds, Acids & Bases Ionic compounds, acids & bases fall apart into ions when they dissolve in water This is called dissociation They conduct electricity when dissolved – this makes them electrolytes. So when we write them as (aq) they are really separated ions in solution EX: NaOH (aq) is really Na + (aq) and OH - (aq) in solution K 2 SO 4 (aq) is really 2 K + (aq) and SO 4 2- (aq) in solution
The ions separate so they can interact and form new products. NOT Solids (s), liquids (l), and gases (g) that form are NOT separated, only aqueous solutions (aq) are separated. To show the details of reactions that involve ions in aqueous solutions chemists use ionic equations.
Complete Ionic Equation This shows ALL the particles in the solutions. Every aqueous compound is written as separate ions All the particles must be accounted for (balanced) Solids, liquids and gases are written as whole compounds (NOT SEPARATED) – we can determine these from the solubility rules! EXAMPLE: MgCl 2 (aq) + PbSO 4 (aq) →MgSO 4 (aq) + PbCl 2 (s) Is really: Mg 2+ (aq) + 2 Cl - (aq) + Pb 2+ (aq) + SO 2- 4 (aq) → Mg 2+ (aq) + SO 2- 4 (aq) + PbCl 2 (s)
Net Ionic Equation This simplifies the complete ionic equation. It includes only the particles that participate in the reaction. It shows the ions that form precipitates, gases, water, or other molecular compounds. We cross out everything that is the same on both sides of the equation.
Ions that do not combine to form a solid, a gas or any other molecular compound are called spectator ions Net ionic equations need to be balanced in terms of both mass (numbers and types of elements) and charge.
Let’s go back to our original example: MgCl 2 (aq) + PbSO 4 (aq) →MgSO 4 (aq) + PbCl 2 (s) Mg 2+ (aq) + 2 Cl - (aq) + Pb 2+ (aq) + SO 2- 4 (aq) → Mg 2+ (aq) + SO 2- 4 (aq) + PbCl 2 (s) Let’s make the net ionic equation – cross out the particles that are the same on both sides of the chemical equation to simplify! Net Ionic Equation: Pb 2+ (aq) + 2Cl - (aq) PbCl 2 (s)
NOW FOR SOME SAMPLE PROBLEMS: Write complete and net ionic equations for the following reactions!
Complete ionic equation: FeBr 3 (aq) + 3 KOH(aq) → 3 KBr (aq) + Fe(OH) 3 (s) Fe 3+ (aq)Br - (aq)3 K + (aq)3 OH - (aq) +++ → + 3 Br - (aq)Fe(OH) 3 (s) + 3 K + (aq)
What is the complete ionic equation for the following chemical equation? BaCl 2 (aq) + Na 2 SO 4 (aq) → BaSO 4 (s) + 2NaCl(aq) a. BaCl 2 (aq) + 2Na + (aq) + SO 4 2- (aq) → 2Na + (aq) + 2Cl - (aq) + BaSO 4 (s) b. Ba 2+ (aq) + Cl - (aq) + Na 2 SO 4 (aq) → Na + (aq) + Cl - (aq) + BaSO 4 (s) c. Ba 2+ (aq) + SO 4 2- (aq) → BaSO 4 (s) d. Ba 2+ (aq) + 2Cl - (aq) + 2Na + (aq) + SO 4 2- (aq) → 2Na + (aq) + 2Cl - (aq) + BaSO 4 (s)
What is the net ionic equation for the following chemical equation? BaCl 2 (aq) + Na 2 SO 4 (aq) → BaSO 4 (s) + 2NaCl(aq) a. BaCl 2 (aq) + 2Na + (aq) + SO 4 2- (aq) → 2Na + (aq) + 2Cl - (aq) + BaSO 4 (s) b. Ba 2+ (aq) + Cl - (aq) + Na 2 SO 4 (aq) → Na + (aq) + Cl - (aq) + BaSO 4 (s) c. Ba 2+ (aq) + SO 4 2- (aq) → BaSO 4 (s) d. Ba 2+ (aq) + 2Cl - (aq) + 2Na + (aq) + SO 4 2- (aq) → 2Na + (aq) + 2Cl - (aq) + BaSO 4 (s)
An equation: Describes a reaction Must be balanced to follow the Law of Conservation of Mass Can only be balanced by changing the coefficients. Has special symbols to indicate state, and if catalyst or energy is required.
Reactions Scientists can tell what type they are by the reactants. Single Replacement happens based on the activity series Double Replacement happens if the product is a solid precipitate, water, or a gas. Use the solubility rules to see which product does not dissolve.
Replacement Reactions A substance will not always replace another in a reaction. This is because substances differ in how they can react with other substances. This mainly occurs with metals and the halogens Use an activity series to see if a reaction will occur. On the activity series the most active elements are at the top and the least are at the bottom.
Predicting Products of Chemical Rxns. & Writing Equations 1. Determine the rxn. type by looking at the reactants. 2. Determine the products based on type 3. Use charges to write formulas of ionic compound & Don’t forget about diatomic elements! 4. Use coefficients to balance the equation.
Solubility Rules 1. All nitrates are soluble. 2. All compounds of Group 1 metals and the ammonium ion, NH 4 +, are soluble. 3. All chlorides are soluble except: AgCl, Hg 2 Cl 2 and PbCl 2. 4. All sulfates are soluble except: PbSO 4, BaSO 4, and SrSO 4.
Solubility Rules 5. All hydroxides and sulfides are insoluble except those of the Group 1 metals and the ammonium ion. 6. All carbonates and phosphates are insoluble except those of the Group 1 metals and the ammonium ion.