Chemical Reactions Chapter 10

Reactions and Equations Section 1 The process by which the atoms of one or more substances are rearranged to form different substances is called a chemical reaction (aka chemical change) Chemical Reaction Indicators Temperature Change (Release/absorption of energy) Color change Odor Gas formation Formation of a solid

Representing Chemical Reactions Reactants- starting substances Products- substances that are formed during the reaction Reactant 1 + Reactant 2  Product 1 + Product 2 “react to produce” or “yield” Always written to the arrow’s right Always written to the arrow’s left

Symbols used in Equations Meaning + Separates two or more reactants or products  Separates reactants from products (s) Identifies solid state (l) Identifies liquid state (g) Identifies gaseous state (aq) Identifies water solution

“Iron and chlorine react to produce iron (III) chloride” Writing Equations “Iron and chlorine react to produce iron (III) chloride” Iron (s) + chlorine (g)  iron (III) chloride (s) Fe (s) + Cl2 (g)  FeCl3 (s) Chemical Equation- statement that uses chemical formulas involved in a chemical reaction Shows the number of atoms of each reactant and each product is equal on both sides of the arrow (balanced)

Practice Problems Write skeleton equations for the following word equations hydrogen (g) + bromine (g)  hydrogen bromide (g) carbon monoxide (g) + oxygen (g)  carbon dioxide (g) potassium chlorate (s)  potassium chloride (s) + oxygen (g)

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Steps for balancing equations Write the skeleton equation for the reaction. Make sure that the chemical formulas are correctly written. Show the physical states of all reactants and products. Count the atoms of the elements in the reactants. If a reaction involves identical polyatomic ions in the reactants and products, count the ions as they are elements. Count the atoms of the elements in the products.

4. Change the coefficients to make the number of atoms equal on both sides of the equations. NEVER change the subscript in a chemical formula to balance an equation because doing so changes the identity of the substance. 5. Write the coefficients in their lowest possible ratio. (whole numbers) 6. CHECK YOUR WORK!

(The reaction occurs in water) Practice Problem Sodium hydroxide and calcium bromide react to produce solid calcium hydroxide and sodium bromide. (The reaction occurs in water)

Organizing Technique Starting Add Coefficients Balanced

Practice Problems Solid zinc and aqueous hydrogen sulfate react to produce hydrogen gas and aqueous zinc sulfate

Classifying Chemical Reactions Section 2 Synthesis-whenever two or more substances combine to form a single product Example: 4Fe(s) + 3 O2(g)  2Fe2O3 (s) General Equation: element/compound + element/compound  compound A + B  AB Combustion- a substance reacts with oxygen to produce carbon dioxide and water Example: CH4(g) + 2O2(g)  CO2(g) + 2 H2O(g) Organic Compound + Oxygen  Carbon Dioxide + Water Organic Compound + O2(g)  CO2 (g) + H2O(g)

Combustion reactions- oxygen combines with a substance and releases energy in the form of heat and light

Example: NH4NO3(s)  N2O(g) + 2H2O(g) Decomposition-a compound breaks down into two or more elements or new compounds Example: NH4NO3(s)  N2O(g) + 2H2O(g) General Equation: compound  two or more elements/compound AB  A + B Practice Problems: The solids aluminum and sulfur react to produce aluminum sulfide. Ethane gas (C2H6) burns in air, producing carbon dioxide gas and water vapor Nickel (II) hydroxide (s) decomposes to produce nickel (II) oxide (s) and water.

Replacement Reactions Single Replacement-one element takes the place of another element in a compound Example: Fe(s) + CuSO4(aq)  FeSO4(aq) + Cu(s) General Equation: element A + compound BX  compound AX + element B A + BX  AX + B HAVE TO USE THE ACTIVITY SERIES TO SEE IF THE METAL WILL BE REPLACED. IF METAL (A) IS LOCATED ABOVE METAL (B), IT WILL REPLACE IT. (IF NOT, WRITE NO REACTION (NR)

Practice Problems K (s) + ZnCl2 (aq)  Cl2 (g) + HF (aq)  Fe (s) + CuSO4 (aq) 

Double-Replacement Reactions Double Replacement- the positive portions for two ionic compounds are interchanged Example: Pb(NO3)2 (aq) + 2KI (aq)  PbI2 (s) + 2KNO3 (aq) General Equation: compound AB + compound CD  compound AD + compound CB AB + CD  AD + CB NOTE: A PRECIPITATE OR WATER MUST BE FORMED!! TO PREDICT THIS, USE THE SOLUILITY RULES TO SEE IF A PRECIPITATE IS FORMED, FOLLOW THE DIRECTIONS TO THE CHART FOR THE COMPOUNDS OF THE PRODUCTS FORMED

Practice Problems Aqueous lithium iodide and aqueous silver nitrate react to produce solid silver iodide and aqueous lithium nitrate. BaCl2(aq) + K2CO3 (aq)

Section Assessment What are the five classes of chemical reactions? Identify two characteristics of combustion reactions. Compare and contrast single-replacement reactions and double-replacement reactions.

Reactions in Aqueous Solutions Section 3 Review: solution = homogeneous mixture Solutes- the particles dissolved in the solution Solvent- water (in most cases)- what does the dissolving Aqueous solution- a solution in which water is the solvent

Three types of products form from the DR-reaction When two aqueous solutions that contain ions as solutes are combined, the ions may react with one another. (double-replacement reaction occurs) Three types of products form from the DR-reaction Precipitate (type of solid) Water Gas

Ionic Equations Complete Ionic Equation- show all of the particles in a solution as they realistically exist Spectator Ions- Ions that do not participate in a reaction Net Ionic Equation- include only the particles that participate in the reaction (forming a precipitate, water and/or gas)

Example Pb(NO3)2 (aq) + 2KI (aq) → 2KNO3 (aq) + PbI2 (s)

Pb+2(aq)+ 2I-(aq)  PbI2(s) Pb(NO3)2 (aq) + 2KI (aq) → 2KNO3 (aq) + PbI2 (s) Complete Ionic Equation: Pb+2(aq)+ 2NO3-1(aq)+ 2K+ (aq)+ 2I-(aq)  2K+(aq) + 2NO3(aq) + PbI2(s) Cross out spectator ions 3. Net Ionic Equation Pb+2(aq)+ 2I-(aq)  PbI2(s)

Your turn! Aqueous solutions of lithium sulfate and calcium nitrate are mixed, forming the precipitate calcium sulfate Steps to remember: Write out complete balanced (DR) reaction (with states) Complete ionic equation Get rid of spectator ions Net ionic equation