Chemical Reactions

Chapter Chemical Reactions O2 H2 react to form? H2O + heat 2006, Prentice Hall CHAPTER OUTLINE          Chemical Reactions Chemical Equation Balancing Equations Types of Chemical Reactions Activity Series of Metals Aqueous Reactions Precipitation Reactions Neutralization and Other Reactions Heat in Chemical Reactions CHEMICAL REACTIONS  A chemical reaction is a rearrangement of atoms in which some of the original bonds are broken and new bonds are formed to give different chemical structures  In a chemical reaction, atoms are neither created, nor destroyed  A chemical reaction, as described above, is supported by Dalton’s postulates CHEMICAL REACTIONS In a chemical reaction, atoms are neither oxygen atoms = oxygen atoms created, nor destroyed CHEMICAL REACTIONS  A chemical reaction can be detected by one of the following evidences: Change of color Formation of a solid Formation of a gas Exchange of heat with surroundings Evidence of Chemical Change Emission of Lightof Heat Color Change Release or Absorption Formation of Solid Formation of aPrecipitate Gas Why use Chemical Equations? Shorthand way of describing a reaction Provides information about the reaction – Formulas of reactants and products – States of reactants and products – Relative numbers of reactant and product molecules that are required – Can be used to determine amounts of the reactants and products CHEMICAL EQUATIONS  A chemical equation is a shorthand expression for a chemical reaction Word equation: Aluminum combines with ferric oxide to form iron and aluminum oxide Chemical equation: Al + Fe2O3  Fe + Al2O3 CHEMICAL EQUATIONS  Reactants are separated from products by an arrow Al + Fe2O3  Fe + Al2O3  Coefficients are placed in front of substances to balance the equation Al + Fe2O3  Fe + Al2O3 Subscripts CHEMICAL EQUATIONS  Reaction conditions are placed over the arrow  Al + Fe2O3  Fe + Al2O3 heat  The physical state of the substances are indicated by the symbols (s), (l), (g), (aq)  Al (s) + Fe2O3 (s)  Fe (l) + Al2O3 (s) solid liquid 10   Example 1: • An gas tank in a home barbecue contains 11.8 x 103 g of propane (C3H8) • Calculate the heat (in kJ) associated with the complete combustion of all of the propane in the tank © 2012 Pearson Education, Inc   Example 1: © 2012 Pearson Education, Inc Classifying Reactions • Also we can classify reactions by what happens: • Redox reactions are the exchange of e • Redox are all reactions except? Note OXIDATION-REDUCTION REACTIONS    Reactions known as oxidation and reduction In an oxidation-reduction reaction, electrons are (redox) havefrom many important applications transferred one substance to another.in our everyday If one substance lives loses electrons, another substance Rusting must gain ofelectrons a nail or the reaction within your car batteries are two examples of redox reactions 64 OXIDATION-REDUCTION REACTIONS    Oxidation is defined as loss of electrons, and reduction is defined as gain of electrons One way to remember these definitions is to use the following mnemonic: Oxidation Is Loss of electrons Reduction Is Gain of electrons OIL RIG Combination, decomposition, single replacement and combustion reactions are all examples of redox reactions 65 OXIDATION-REDUCTION REACTIONS  In atoms offormation metals lose Forgeneral, example, in the of electrons calcium to form cations, and areand therefore sulfide from calcium sulfur oxidized, while atomsCa of +non-metals gain electrons to S CaS form anions, and are therefore reduced Ca Ca2+ + e- S + e- S2- Oxidation Reduction  Therefore, the formation of calcium sulfide involves two half-reactions that occur simultaneously, one an oxidation and the other 66 a reduction COMBUSTION  A reaction that involves oxygen as a reactant and produces large amounts of heat is classified occurs in as a combustion reaction the cylinders of the engine  Combustion reactions are a subclass of Oxidation-Reduction reactions C8H18(g) + 25 O2(g)  16 CO2(g) + 18 H2O(g) 67 Combustion Products • predicting the products of a combustion reaction; simply combine each element in the other reactant with oxygen Reactant Combustion Product contains C CO2(g) contains H H2O(g) contains S SO2(g) contains N NO(g) or NO2(g) contains metal M2On(s) Combustion Reactions • combustion reactions are always exothermic • in combustion reactions, O2 combines with the elements in another reactant to make the products Fe(s) + O2(g) → Fe2O3(s) + energy CH4(g) + O2(g) → CO2(g) + H2O(g) + energy The flame on a gas stove results from the oxidation of carbon in natural gas Reverse of Combustion Reactions • since combustion reactions are exothermic, their reverse reactions are endothermic • the reverse of a combustion reaction involves the production of O2 energy + Fe2O3(s) → Fe(s) + O2(g) energy + CO2(g) + H2O(g) → CH4(g) + O2(g) • reactions in which O2 is gained or lost are redox reactions REDOX IN BIOLOGICAL SYSTEMS  Many important biological reactions involve oxidation and reduction  In these reactions, oxidation involves addition of oxygen or loss of hydrogen, and reduction involves Oxidation loss of oxygen or gain of hydrogen (loss of  For example, poisonous methyl alcohol is hydrogen) metabolized by the body by the following reaction: CH3OH methyl alcohol H2CO + 2H• formaldehyde 71 REDOX IN BIOLOGICAL SYSTEMS  The formaldehyde is further oxidized to formic acid and finally carbon dioxide and water byOxidation the following reactions: (gain of H2CO + O2 formaldehyde H2CO2 + O2 2H2CO2 oxygen) formic acid CO2 + H2O formic acid 72 REDOX IN BIOLOGICAL SYSTEMS  In Themany oxidation biochemical of a typical oxidation-reduction biochemical molecule reactions, can the transfer involve the transfer of hydrogen of two atoms hydrogen produces atoms energy to a in the cells proton acceptor such as coenzyme FAD to produce its reduced form FADH2 73 REDOX IN BIOLOGICAL SYSTEMS  In summary, the particular definition of oxidationreduction depends on the process that occurs in the reaction 74 THE END 75