Chemical Equations and Reactions Chapter 8 General Chemistry Ch. 8 Chemical Eq and React Gen Chem

Chemical Reactions Basics Ch. 8 Chemical Eq and React Gen Chem

Chemical Reactions A chemical reactions are ______________________. Recall: chemical changes are when one or more substances are changed into different substances Examples: wood burning, metal rusting Ch. 8 Chemical Eq and React Gen Chem

Indications of a Chemical Reaction Certain easily observed changes indicate that a chemical reaction has occurred: _______________by heat and/or light color change production of _________ production of __________ A solid that is produced as a result of a chemical reaction in solution and that separates from the solution is known as a precipitate Ch. 8 Chemical Eq and React Gen Chem

Law of Conservation of Matter Chemical reactions obey the Law of Conservation of Matter in all chemical and physical changes, matter is neither created or destroyed ____________________________________________________________________ Ch. 8 Chemical Eq and React Gen Chem

Chemical Equations A chemical equation represents, with symbols and formulas, the identities and the amounts of the reactants and products in a chemical reaction. Has two parts: Reactants: __________________________ Products: ____________________________ The reactants turn into the products 4 Fe + 3 O2  2 Fe2O3 Reactants  products Ch. 8 Chemical Eq and React Gen Chem

Ways to Express a Chemical Reaction The way atoms are joined is changed in a chemical reaction. Can be described several ways: 1. In a sentence Copper reacts with chlorine to form copper (II) chloride. 2. In a word equation Copper + chlorine ® copper (II) chloride 3. In formula equation: Cu + Cl2  CuCl2 Ch. 8 Chemical Eq and React Gen Chem

Symbols Used in Chemical Equations Ch. 8 Chemical Eq and React Gen Chem

Additional Symbols Used in Equations shows that heat is supplied to the reaction is used to indicate a catalyst is supplied, in this case, platinum. Ch. 8 Chemical Eq and React Gen Chem

What is a catalyst? A catalyst is _______________ ___________________, without being changed or used up by the reaction. Enzymes are biological or protein catalysts. Ch. 8 Chemical Eq and React Gen Chem

Study Buddy Review What are four things that indicate a chemical reaction has taken place? What is the Law of Conservation of mass? What does the symbol (l) mean? What does (aq) mean? Ch. 8 Chemical Eq and React Gen Chem

Balancing Chemical Equations Ch. 8 Chemical Eq and React Gen Chem

Skeleton and Balanced Equations _____________________do not indicate how many of each element/compound _______________________the number of atoms of each element is the same on both sides of the reaction. Ch. 8 Chemical Eq and React Gen Chem

Numbers in Balanced Equations Use coefficients to balance equation Coefficients: _______________________ ______________which represents number of units of that compound Subscript: small whole number placed in chemical formula to represent number of atoms of an element in a compound Ch. 8 Chemical Eq and React Gen Chem

4 Fe + 3 O2  2 Fe2O3 subscript Coefficient Ch. 8 Chemical Eq and React Gen Chem

Balanced Equation A balanced equation has the _____________________ of each element on both sides of the equation Atoms can’t be created or destroyed All the atoms at the beginning must appear in the end Ch. 8 Chemical Eq and React Gen Chem

® O + C C O O C + O2 ® CO We need one more oxygen in the products. Can’t change the formula, because it describes what it is (carbon monoxide in this example) Ch. 8 Chemical Eq and React Gen Chem

® Must be used to make another CO But where did the other C come from? + C O C O Must be used to make another CO But where did the other C come from? Ch. 8 Chemical Eq and React Gen Chem

® Must have started with two C 2 C + O2 ® 2 CO C C O O + O C C O Ch. 8 Chemical Eq and React Gen Chem

Rules for balancing: Assemble, write the correct formulas for all the reactants and products Count the number of atoms of each type of element appearing on both sides Balance the atoms of an element one at a time by adding coefficients (the numbers in front) - save H and O until LAST! Check to make sure it is balanced. Ch. 8 Chemical Eq and React Gen Chem

Never Never change a subscript to balance an equation. If you change the formula you are describing a different reaction. H2O is a different compound than H2O2 Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not. Ch. 8 Chemical Eq and React Gen Chem

Balancing Equations Examples H2 (g) + O2 (g)  H2O (l) Zn + HCl  H2 + ZnCl2 Pb (NO3)2 + K2S  PbS + KNO3 Ch. 8 Chemical Eq and React Gen Chem

Word Equation Examples Write a balanced chemical equation for the following: Aqueous solutions of sulfuric acid and sodium hydroxide react to form aqueous sodium sulfate and water. Ch. 8 Chemical Eq and React Gen Chem

Five General Types of Chemical Reactions Ch. 8 Chemical Eq and React Gen Chem

Five General Types of Chemical Reactions Synthesis (Composition) ________________________ Single-Replacement Combustion By knowing the type of reaction that is occurring, you can predict the products that will be formed. Ch. 8 Chemical Eq and React Gen Chem

General Types of Chemical Reactions Combination: A + B  AB Decomposition: AB  A + B Single Replacement : AX +B  A + BX Double Replacement: AX + BY  AY + BX Combustion: CxHy + O2  CO2 + H2O

Synthesis (Combination) General form: A + B  AB ____________________________ A, B = elements or compounds AB = compound consisting of A and B This is the only type of chemical reaction in which there is a single product formed. This single product is always more complex than the reactants. Ch. 8 Chemical Eq and React Gen Chem

Examples of Synthesis Reactions a. calcium + oxygen yields calcium oxide 2Ca + O2  2CaO b. carbon dioxide + water yields carbonic acid CO2 + H2O  H2CO3 Notice: All equations show two (or more) reactants, but only one product. http://www.ric.edu/ptiskus/reactions/Index.htm Ch. 8 Chemical Eq and React Gen Chem

Decomposition Reactions (Decomposing = breaking down into smaller parts; microorganisms) _______________________________ ______________________________The opposite of direct combination/synthesis. You can identify this reaction because there is only one reactant. General form: AB  A + B AB = compound A, B = elements or simpler compounds Ch. 8 Chemical Eq and React Gen Chem

Examples of Decomposition Reactions Water yields hydrogen and oxygen 2H2O  2H2 + O2 marble (rock) yields (with heating) calcium oxide and carbon dioxide CaCO3  CaO + CO2 Notice: single compound decomposes into two (or more) products. http://www.ric.edu/ptiskus/reactions/Index.htm Ch. 8 Chemical Eq and React Gen Chem

Single-Replacement Reactions __________________________________________________________ General Form: A + BX  AX + B AX, BX = ionic compounds A, B = elements X = ion that switches partners Ch. 8 Chemical Eq and React Gen Chem

Examples of Single-Replacement Reactions Magnesium metal and copper (II) sulfate Mg + CuSO4  MgSO4 + Cu Iron metal and copper (II) sulfate) Fe + CuSO4  FeSO4 + Cu www.ric.edu/ptiskus/reactions/Index.htm Ch. 8 Chemical Eq and React Gen Chem

Double-Replacement Reactions ______________________________________________________________ Look for: 2 compounds as reactants and 2 compounds as products. Reactants are usually ionic compounds. Specific example: neutralization reactions between acid and base General form: AX + BY  AY + BX (Notice: X and Y “change partners”) Ch. 8 Chemical Eq and React Gen Chem

Examples of Double Replacement Reactions Calcium carbonate and hydrochloric acid yield calcium chloride and carbonic acid. CaCO3 + 2HCl  CaCl2 + H2CO3 www.ric.edu/ptiskus/reactions/Index.htm Ch. 8 Chemical Eq and React Gen Chem

Rules of Double-Displacement Reactions Reactants must be dissolved in water (releasing the ions). Will occur if: ______________________________ _____________________ Ch. 8 Chemical Eq and React Gen Chem

C2H5OH (gasohol) + 3O2  3H2O + 2CO2 Combustion Reactions Reactants: a fuel (usually a hydrocarbon) and oxygen. Products: water, carbon dioxide, and lots of energy! (heat, light) Examples: CH4 (methane) + 2O2  2H2O + CO2 C2H5OH (gasohol) + 3O2  3H2O + 2CO2 www.ric.edu/ptiskus/reactions/Index.htm Ch. 8 Chemical Eq and React Gen Chem

Study Buddy Review Describe each of the following to your study buddy: Synthesis (combination) Decomposition Single-Replacement Double-Replacement Combustion Ch. 8 Chemical Eq and React Gen Chem

Activity Series Ch. 8 Chemical Eq and React Gen Chem

Activity Series and Single Replacement Reactions Al + CuCl2  ??? Cu + AlCl3  ??? Only one of the following reactions will occur How do you know which one? Ch. 8 Chemical Eq and React Gen Chem

Activity Series of Metals Ch. 8 Chemical Eq and React Gen Chem http://wps.prenhall.com/wps/media/objects/165/169060/tool0403.gif

Ch. 8 Chemical Eq and React Gen Chem

Activity Series Rules Elements at top of series are most active Elements at bottom of series are least active (coinage metals) __________________________________________________________ Example: Al + CuCl2  will occur Cu + AlCl3  will NOT occur Ch. 8 Chemical Eq and React Gen Chem

Activity Series Examples Using the activity series, predict whether each of the possible reactions will occur: Cr + H2O  Pt + O2  Cd + 2HBr  Ch. 8 Chemical Eq and React Gen Chem

References Dr. Stephen L. Cotton Charles Page High School Mrs. Lijek Ch. 8 Chemical Eq and React Gen Chem