Chapter 11 CHEMICAL REACTIONS

Transcription

1 Chapter 11 CHEMICAL REACTIONS Get pumped Chemical Equations A Chemical equation is a representation of a chemical reaction with formulas of the reactants on the left and formulas of the products on the right. Catalysts Definition: a substance that speeds up the reaction but is not used up in the reaction It is not a reactant nor a product, so it is written on top of the arrow H 2 O 2 (aq) MnO 2 H 2 O(l) + O 2 (g) Step 1: Determine formulas of the reactants and products Example-Methane and oxygen react to form carbon dioxide and water. Reactants: CH 4 and O 2 Products: CO 2 and H 2 O Step 2: Write the Skeleton equation (does not indicate the relative amounts of the reactants and products) CH 4 + O 2 CO 2 + H 2 O 1

2 Step 3: Count the number of atoms of each element in the reactants and products. Step 4: Add coefficients to reactants or products until atoms of each element are d. CH 4 + O 2 CO 2 + H 2 O 1 C 1 C 4 H 2 H 2 O 3 O CH 4 + 2O 2 CO 2 + 2H 2 O 1 C 1 C 4 H 4 H 4 O 4 O In-Class Examples 1. Al + O 2 Al 2 O 3 2. C 3 H 8 + O 2 CO 2 + H 2 O 3. Al(NO 3 ) 3 + NaOH Al(OH) 3 + NaNO 3 4. KNO 3 KNO 2 + O 2 Signs of a chemical reaction Production of heat and/or light Endothermic: takes in heat (gets colder) Exothermic: gives off heat (feels warmer) Formation of a gas Formation of a precipitate Color change 5. BaF 2 + K 3 PO4 Ba 3 (PO 4 ) 2 + KF 2

3 Liquid vs. Aqueous NaCl(l) NaCl(aq) Diatomic elements There are 7 elements that do not exist as a single atom. They are bonded to another atom when they are in the elemental state. Types of Chemical Reactions CHAPTER 11.2 Combination Reactions 2 or more substances react to form a single new substance Examples: 2Mg(s) + O 2 (g) 2MgO (s) SO 2 (g) + H 2 O (l) H 2 SO 3 (aq) N 2 + O 2 Decomposition Reaction A single compound breaks down into two or more simpler products. Examples: 2NaN 3 (s) 2Na (s) + 3N 2 (g) H 2 CO 3 (aq) H 2 O (l) + CO 2 (g) 3

4 NaCl(s) Single-Replacement Reaction One element replaces a second element in a compound. Both the reactants and the products consist of an element and a compound. Examples: 2K (s) + 2 H 2 O (l) 2KOH (aq) + H 2 (g) Zn (s) + Cu(NO 3 ) 2 (aq) Cu (s) + Zn(NO 3 ) 2 (aq) Activity Series of Metals A reactive metal can only replace a metal listed below it in the activity series. KI + Cl 2 Example: zinc can replace tin, but tin cannot replace zinc Double-replacement Reaction An exchange of positive ions between two compounds. Indicators of Double-replacement A precipitate is formed (s) A gas is produced (g) One product is a molecular compound (water) Mg(NO 3 ) 2 + K 3 PO 4 Examples: Na 2 S (aq) + Cd(NO 3 ) 2 (aq) CdS(s) + 2NaNO 3 (aq) 2NaCN (aq) + H 2 SO 4 (aq) 2HCN (g) + Na 2 SO 4 (aq) 4

5 Medical Oxygen Tank Safety Precautions around oxygen tanks are as follows: Keep the tanks at least ten feet from stoves, fireplaces, candles or any other open flame. Do not smoke while on oxygen therapy, and do not allow others to smoke near you. Do not use electric razors near oxygen tanks due to the potential for sparks. Do not use oil, grease or other petroleum-based productson or near the tank, and do not use petroleum-based products on your skin while using the tank. Mark each room where you have a tank with signs stating there are oxygen cylinders in use. Ensure that all the smoke detectors in the house are working. Alert the fire department and all utility companies that there ishome oxygen therapy in use. They can help if there is a loss of power or failure of service. Keep tubing well out of the way,and do not let it become bound up in furniture or create a tripping hazard. *taken from Inogen.com (Home Respiratory Therapy) Combustion Reactions A hydrocarbon reacts with oxygen, producing carbon dioxide and water Often heat or light are produced C 2 H 6 + O 2 Example: 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O(g) Practice Balance the equation and name the type of reaction. 1) Hydrogen combines with oxygen to produce water. 2) Sodium reacts with magnesium chloride, yielding sodium chloride and magnesium. 3) Aluminum bromide and chlorine react to form aluminum chloride and bromine. 4) Aluminum nitrate and sodium sulfide react to form aluminum sulfide and sodium nitrate. Reactions in Aqueous Solution CHAPTER

6 Net Ionic Equation a net ionic equation is an equation for a reaction in solution that shows only those particles directly involved in the chemical change (AKA we don t care about all the extra stuff ) But don t worry, it s still d in mass and charge! How to write a net ionic equation 1. Write out the COMPLETE IONIC EQUATION a) Shows dissolved ionic compounds as dissociated free ions Original equation: AgNO 3 (aq) + NaCl(aq) AgCl (s) + NaNO 3 (aq) Complete Ionic: Ag + (aq) + NO 3 (aq) + Na + (aq) + Cl - (aq) AgCl (s) + Na + (aq) +NO 3- (aq) How to write a net ionic equation Step 2: Eliminate ions that appear unchanged on both sides of the equation Complete Ionic: Ag + (aq) + NO 3 (aq) + Na + (aq) + Cl - (aq) AgCl (s) + Na + (aq) +NO 3- (aq) Ag + (aq) + Cl - (aq) AgCl (s) What remains is your NET IONIC EQUATION 6