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UNIT 5 Chemical Reactions, Rates, and Equilibrium

UNIT 5 Chemical Reactions, Rates, and Equilibrium. Chapters 8, 17, and 18. Chemical Equations and Reactions. Chapter 8. Chapter 8 – Section 1 : Describing Chemical Reactions. What Is a Chemical Reaction?.

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UNIT 5 Chemical Reactions, Rates, and Equilibrium

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  1. UNIT 5Chemical Reactions, Rates, and Equilibrium Chapters 8, 17, and 18

  2. Chemical Equations and Reactions Chapter 8

  3. Chapter 8 – Section 1: Describing Chemical Reactions What Is a Chemical Reaction? • Achemical reactionis the process by which one or more substances are changed into one or more different substances. • In any chemical reaction, the original substances are known as the reactantsand the resulting substances are known as the products. Visual Concept

  4. Chapter 8 – Section 1: Describing Chemical Reactions The Law of Conservation of Mass • According to the law of conservation of mass, the total mass of reactants must equal the total mass of products for any given chemical reaction. Visual Concept

  5. Chapter 8 – Section 1: Describing Chemical Reactions Indications of a Chemical Reaction Signs that a chemical reaction is taking place: • Release of energy as heat and/or light. • Production of a gas. • Formation of a precipitate. • Precipitate - a solid that separates from a liquid solution. • Color change. Visual Concept

  6. Chapter 8 – Section 1: Describing Chemical Reactions Chemical Equations • A chemical equation represents a chemical reaction using symbols and formulas. Example: • 2H2O(l) 2H2(g) + O2(g) Products Reactants

  7. Chapter 8 – Section 1: Describing Chemical Reactions Rules for Writing Chemical Equations • The equation must represent known facts. • The equation must contain the correct formulas for the reactants and products. • The law of conservation of mass must be satisfied.

  8. Chapter 8 – Section 1: Describing Chemical Reactions Word Equations • The first step in writing a chemical equation is to identify the facts. • In a word equationthe reactants and products are represented by words. • A word equation is qualitative. Example: methane + oxygen carbon dioxide + water

  9. Chapter 8 – Section 1: Describing Chemical Reactions Formula Equations • The next step is to replace the names of the reactants and products with symbols and formulas. • A formula equation represents the reactants and products of a chemical reaction by their symbols or formulas. Example: CH4(g) + O2(g) CO2(g) + H2O(g)

  10. Chapter 8 – Section 1: Describing Chemical Reactions Diatomic Molecules • Oxygen gas (O2) is an example of an element that normally exists as a diatomic molecule. You need to memorize all seven:

  11. Chapter 8 – Section 1: Describing Chemical Reactions Symbols used in Chemical Equations

  12. Chapter 8 – Section 1: Describing Chemical Reactions Word and Formula EquationsSample Problem Write word and formula equations for the reaction that occurs when solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper(II) nitrate. Solution: Word Equation: Formula Equation: (not balanced) → copper + silver nitrate silver + copper(II) nitrate → Ag(s) Cu(s) + AgNO3(aq) + Cu(NO3)2(aq)

  13. Chapter 8 – Section 1: Describing Chemical Reactions Balancing Equations • The final step in writing correct chemical equations is to make sure the law of conservation of mass is satisfied. • The numbers and types of atoms on both sides of the equation must be the same – this is called balancing an equation. • Equations are balanced by inserting coefficients - whole numbers that appear in front of formulas in a chemical equation. Visual Concept

  14. Chapter 8 – Section 1: Describing Chemical Reactions Balancing EquationsSample Problem A Balance the following equation: CH4(g) + O2(g) CO2(g) + H2O(g) Solution: • Start with the easiest element…carbon. • Carbon is already balanced. • Next count the hydrogen atoms. • Two more hydrogen atoms are needed on the right. • Finally, count oxygen atoms. • There are 4 oxygens on the right side of the equation, but only two on the left. • Add a coefficient 2 in front of the O2 on the left. 2 2

  15. Chapter 8 – Section 1: Describing Chemical Reactions Balancing EquationsSample Problem B Balance the following equation: Al4C3(s) + H2O(l) CH4(g) + Al(OH)3(s) Solution: • Let’s start with aluminum. • Add a coefficient 4 to Al(OH)3 on the right. • Next count the carbon atoms. • Add a coefficient 3 to CH4 on the right. • Balance the oxygen atoms. • Add a 12 to the H2O on the left. • Lastly, count the hydrogen atoms. • Hydrogen is already balanced. 3 12 4

  16. Chapter 8 – Section 2: Types of Chemical Reactions Types of Chemical Reactions • There are 5 basic types of chemical reactions: • Synthesis • Decomposition • Single-Displacement • Double-Displacement • Combustion Visual Concept

  17. Chapter 8 – Section 2: Types of Chemical Reactions Synthesis Reactions • In a synthesis reaction (also called a composition reaction) 2 or more substances combine to form a new compound. • This type of reaction is represented by the following general equation: A + X AX

  18. Chapter 8 – Section 2: Types of Chemical Reactions Synthesis - Examples • 2Mg(s) + O2(g) 2MgO(s) • S8(s) + 8O2(g) 8SO2(g) • 2H2(g) + O2(g) 2H2O(g) • 2Na(s) + Cl2(g) 2NaCl(s) • Mg(s) + F2(g) MgF2(s)

  19. Chapter 8 – Section 2: Types of Chemical Reactions Decomposition Reactions • In a decomposition reaction, a single compound breaks apart to form 2 or more simpler substances. • Decomposition is the opposite of synthesis. • This type of reaction is represented by the following general equation: AX A + X

  20. Chapter 8 – Section 2: Types of Chemical Reactions Decomposition - Examples electricity • 2H2O(l) 2H2(g) + O2(g) • CaCO3(s) CaO(s) + CO2(g) • H2CO3(aq) CO2(g) + H2O(l) • 2HgO(s) 2Hg(l) + O2(g) • Ca(OH)2(s) CaO(s) + H2O(g) ∆ ∆ ∆

  21. Chapter 8 – Section 2: Types of Chemical Reactions Single-Displacement Reactions • In a single-displacement reaction (also called single-replacement) one element replaces a similar element in a compound. • They often take place in aqueous solution. • This type of reaction is represented by the following general equation: A + BX AX + B

  22. Chapter 8 – Section 2: Types of Chemical Reactions Single Displacement - Examples • 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) • 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g) • Mg(s) + 2HCl(aq) H2(g) + MgCl2(aq) • Cl2(g) + 2KBr(aq) 2KCl(aq) + Br2(l) • F2(g) + 2NaCl(aq) 2NaF(aq) + Cl2(g)

  23. Chapter 8 – Section 2: Types of Chemical Reactions Double-Displacement Reactions • In double-displacement reactions, the ionsof 2 compounds exchange places in an aqueous solution to form 2 new compounds. • One of the compounds formed is usually either a precipitate, a gas, or water. • Represented by the following general equation: AX + BY AY + BX

  24. Chapter 8 – Section 2: Types of Chemical Reactions Double Displacement - Examples • Formation of a Precipitate 2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq) • Formation of a Gas FeS(s) + 2HCl(aq) H2S(g) + FeCl2(aq) • Formation of Water HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

  25. Chapter 8 – Section 2: Types of Chemical Reactions Combustion Reactions • In a combustion reaction, a fuel combines with oxygen, releasing a large amount of energy in the form of light and heat. • Products of combustion reactions are always carbon dioxide and water vapor. • Example:Combusion of propane C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

  26. Chapter 8 – Section 2: Types of Chemical Reactions Types of ReactionsSample Problem Classify each of the following reactions as a synthesis, decomposition, single-displacement, double-displacement, or combustion reaction. • N2(g) + 3H2(g) → 2NH3(g) • 2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g) • 2NaNO3(s) → 2NaNO2(s) + O2(g) • 2C6H14(l) + 19O2(g) → 12CO2(g) + 14H2O(l) synthesis single-displacement decomposition combustion

  27. Chapter 8 – Section 3: Activity Series of the Elements Chemical Activity • The ability of an element to react is referred to as the element’s activity. • The more easilyan element reactswith other substances, the greater its activity is. Li Au

  28. Chapter 8 – Section 3: Activity Series of the Elements Activity Series • An activity seriesis a list of elements organized by their chemical activity. • The most-active element is placed at the top in the series. • It can replace each of the elements below it in a single-displacement reaction. • Activity series can be used to predict whether a chemical reaction will occur. • Activity series are based on experiment.

  29. Chapter 8 – Section 3: Activity Series of the Elements Activity Series (continued)

  30. Chapter 8 – Section 3: Activity Series of the Elements Activity SeriesSample Problem Use the activity series to predict whether or not there will be a reaction for the possibilities below. If a reaction will occur, write the products and balance the equation. • Ni(s) + Pb(NO3)2(aq) → ____ • MgCl2(aq) + Zn(s) →_____ • Br2(l) + KI(aq) → _____ • Cu(s) + HCl(aq) → _____ Pb(s) + Ni(NO3)2(aq) Yes No reaction 2 I2(l) + KBr(aq) 2 Yes No reaction

  31. Reaction Kinetics & Chemical Equilibrium Chapters 17 & 18

  32. Chapter 17 – Section 1: The Reaction Process Collision Theory • Collision Theory says that in order for reactions to occur between substances, particles must collide. • For a collision to be effective, the particles must: • Collide with sufficient energy. • Have a favorable orientation.

  33. Chapter 17 – Section 1: The Reaction Process Activation Energy • Energy is needed to overcome the repulsion forces between molecules and transform the reactants into an activated complex. • Activation energyis the minimum energy required to get a reaction started.

  34. Chapter 17 – Section 2: Reaction Rate Rate-Influencing Factors • The rate of a chemical reaction depends on the number of collisions between particles. • Rate-influencing factors are: • Nature of Reactants • Surface Area • Temperature • Concentration • Presence of Catalysts Visual Concept High Concentration Low Concentration

  35. Chapter 18 – Section 1: The Nature of Chemical Equilibrium Reversible Reactions • A chemical reaction in which the products can react to re-form the reactants is called areversible reaction. • A reversible reaction is written using double arrows to show that the reaction is proceeding in both directions. Example:

  36. Chapter 18 – Section 1: The Nature of Chemical Equilibrium Chemical Equilibrium • A reversible reaction is in chemical equilibriumwhen the rate of its forward reaction equals the rate of its reverse reaction and the concentrations of its products and reactants remain unchanged. • At equilibrium, both reactions continue, but there is no net change in the composition of the system. Visual Concept

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