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Chemical Reactions

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

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Chemical Reactions

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  1. Chemical Reactions Chapter 10

  2. Reactions and EquationsSection 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

  3. 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

  4. Symbols used in Equations

  5. 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)

  6. 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)

  7. Page 282 4-6

  8. 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.

  9. 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!

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

  11. Organizing Technique Starting Add Coefficients Balanced

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

  13. Classifying Chemical ReactionsSection 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) • General Equation: Organic Compound + Oxygen  Carbon Dioxide + Water Organic Compound + O2(g) CO2 (g) + H2O(g)

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

  15. 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.

  16. 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)

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

  18. 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

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

  20. 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.

  21. Reactions in Aqueous SolutionsSection 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

  22. 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

  23. 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)

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

  25. 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 Pb+2(aq)+ 2NO3-1(aq)+ 2K+(aq)+ 2I-(aq) 2K+(aq) + 2NO3(aq) + PbI2(s) 3. Net Ionic Equation Pb+2(aq)+ 2I-(aq) PbI2(s)

  26. 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

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