CHEMICAL REACTIONS Reactants: Zn + I 2 Product: Zn I 2 Unit 2 Chemical Reactions The unit 2 exam will cover material from multiple chapters. You are responsible for the following from your text on exam 2. Chapter Sections 3 3.1, 3.2 4 4.1-4.4 20 20.1-20.2 There are three ways we write chemical equations 1. Molecular Equations 2. Full Ionic Equations 3. Net Ionic Equations On the national exam, you will see both Molecular and Net Ionic Equations. From now on, you should pay close attention to which form of chemical equation is requested in each problem. Law of Conservation of Mass We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends. --Antoine Lavoisier, 1789 2012 Pearson Education, Inc. Anatomy of a Chemical Equation CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) Anatomy of a Chemical Equation CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) Reactants appear on the left side of the equation. Products appear on the right side of the equation. The states of the reactants and products are written in parentheses to the right of each compound.
Anatomy of a Chemical Equation CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) Subscripts and Coefficients Give Different Information Coefficients are inserted to balance the equation. Subscripts tell the number of atoms of each element in a molecule. Coefficients tell the number of molecules. Today, we will focus on Molecular Equations Gives overall reaction in terms of the parent species, but NOT necessarily the actual forms of reactants & products undergoing a chemical change. (misleading) Must be balanced Should include the correct physical states Molecular Equations Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 Balancing Equations C 3 H 8 (g) + O 2 (g) CO 2 (g) + H 2 O(g) B 4 H 10 (g) + O 2 (g) B 2 O 3 (g) + H 2 O(g) Representing Physical States for Reactants and Products Physical states can be identified for all types of matter: 1. Atoms and Elements 2. Ionic Compounds (ions) 3. Molecules
Physical States at Room Temperature All metal atoms are solids except Hg and Ga. Physical States at Room Temperature Non-metals atoms (including di- and polyatomic elements) and can be (s), (l) or (g). Physical States at Room Temperature All natural ionic compounds are solids NaCl Crystal Lattice Physical States at Room Temperature Ionic compounds can sometimes dissociate into solution Solutions are defined as homogeneous mixtures of two or more pure substances. The solvent is present in greatest abundance. All other substances are solutes. Dissociation When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. This process is called dissociation. Water Solubility of Ionic Compounds Ionic compounds, commonly called salts, have varying solubilities. See Table 4.1 on pg. 121. Solubility refers the the amount of a substance that can be dissolved in a given quantity of solvent at a given temperature.
Water Solubility of Ionic Compounds If the attractions between solvent particles for the solute particles is stronger than the attractions between solute particles, the solute particles can go into solution and are said to be soluble. If the attractions between solute particles are too great, the substance is said to insoluble. Handout Solubility of Salts in Water 1. Most nitrate salts are soluble 2. Most salts containing the alkali metal ions and the ammonium ion are soluble 3. Most chloride, bromide, and iodide salts are soluble, EXCEPT of salts containing the ions of silver, lead (ll), and mercury (l) Solubility of Salts in Water 4. Most sulfate salts are soluble, EXCEPT with ions of barium, lead (Il), mercury (ll), and calcium 5. Most hydroxide salts are only slightly soluble. The important soluble hydroxides are NaOH and KOH. Barium, strontium, and calcium hydroxides are marginally soluble Solubility of Salts in Water 6. Most sulfide, carbonate, chromate, and phosphate salts are only slightly soluble Memorize Patterns On Solubility Handout Physical States at Room Temperature Molecules can be (s), (l) or (g). Physical States at Room Temperature Molecules can sometimes be dissolved or ionized into solution Some molecules dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugar ethanol ethylene glycol
Dissolution Electrolytes and Nonelectrolytes An electrolyte is a substance that dissociates into ions when dissolved in water. A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so. Soluble ionic compounds tend to be electrolytes. Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases. ACIDS & BASES Acids and bases are molecules that are ionized by the loss or addition of hydrogen nuclei in the presence of a solvent Acid: Base: HCl(aq) ---> H + (aq) + Cl - (aq) NaOH(aq) Na + (aq) + OH - (aq) Arrhenius acid is a substance that produces H + (H 3 O + ) in water STRONG ACIDS Arrhenius base is a substance that produces OH - in water Movie Some strong acids are: HCl hydrochloric H 2 SO 4 sulfuric HClO 4 perchloric HNO 3 nitric There are seven strong acids total. A strong acid is a strong electrolyte; therefore, it completely ionizes in solution HNO 3
Weak Acids Acetic acid ionizes only to a small extent, so it is a weak electrolyte. Electrolytes A strong electrolyte dissociates completely when dissolved in water. A weak electrolyte only dissociates partially when dissolved in water. CH 3 CO 2 H (aq) CH 3 CO 2 - (aq) + H + (aq) Monoprotic acid: HCl HCl(aq) + NaOH(aq) H 2 O(l) + NaCl(aq) H + + Cl - + Na + + OH - H + + OH - H 2 O H 2 O + Na + + Cl - diprotic acid: H 2 SO 4 H 2 SO 4 (aq) + 2NaOH(aq) 2H 2 O(l) + Na 2 SO 4 (aq) H + + OH - H 2 O polyprotic acid: H 3 PO 4 H 3 PO 4 (aq) + 3NaOH(aq) 3H 2 O(l) + Na 3 PO 4 (aq) H 3 PO 4 + 3 OH - 3 H 2 O + PO 4 3- Ammonia, NH 3 An Important Weak Base
Strong acids Strong bases Soluble ionic salts Strong Electrolytes Are Know the strong acids & bases! Some Simple Patterns of Chemical Reactions Based on: What atoms do in a chemical reaction. What type of products are formed Synthesis A.K.A. (combination) A + B AB elements compounds Any atom or group of atoms combine to form a more complex compound Decomposition AB A + B elements compound and/or simpler compounds A compound is broken down into simpler substances Single Displacement A + BX AX + B a more reactive element replaces a less reactive element in a compound (involves ions) Predicted using the Activity Series (get out your activity series)
Double Displacement AX (aq) + BY (aq) AY (?) + BX (?) Exchange of ions between two or more compounds Precipitation Reactions Neutralization Reactions Double Displacement Reactions Combustion Substance + O 2 Oxide of Elements hydrocarbon + O 2 CO 2 + H 2 O Oxides are formed from each element in the compound being combusted. A hydrocarbon in combustion reactions refer to only carbon, hydrogen and oxygen containing compounds