Ch 4 Chemical Reactions HCR BB notes

Ch 4 Chemical Reactions HCR BB notes - 1 CHE 1301 Petrucci,...

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Unformatted text preview: 1 CHE 1301 Petrucci, Harwood, Herring, Madura Chapter 4: Chemical Reactions Dr. Bruce E. Hodson 2 Chemical Change (a.k.a. Chemical Reaction ) : changes resulting in altered composition and/or molecular structure (new substances formed). 1.2 Physical and Chemical Changes 3 4.1 Chemical Reactions and Chemical Equations 4 4.1 Chemical Reactions and Chemical Equations Color Change Formation of Solid Precipitate Formation of a Gas Emission of Light Release or Absorption of Heat Usually accompanied by macroscopic phenomena. 5 4.1 Chemical Reactions and Chemical Equations We often need to look to the microscopic (atomic) level to make sure a chemical change has occurred . Is boiling water a chemical change ? 6 4.1 Chemical Reactions and Chemical Equations Chemical reactions are represented by chemical equations . CH 4 + 2 O 2 CO 2 + 2 H 2 O Reactants Products Note: When a substance reacts with oxygen, forming one or more oxygen-containing compounds and emitting heat it is called combustion 7 4.1 Chemical Reactions and Chemical Equations The equation must be balanced using Stoichiometric Coefficients CaSO 3( s ) + 2 HCl ( aq ) CaCl 2( aq ) + SO 2( g ) + H 2 O ( l ) NaCl ( aq ) ( g ) = gas; ( l ) = liquid; ( s ) = solid; ( aq ) = aqueous = dissolved in water; = heat; h = light 8 4.1 Chemical Reactions and Chemical Equations We cannot create or destroy atoms (matter), hence we balance the number of atoms on each side of a chemical equation .. Hydrogen + Oxygen Water + Heat 9 The equation is balanced by adding coefficients not by changing the equation and not by changing the formulae. 4.1 Chemical Reactions and Chemical Equations 10 1. Write a skeletal equation by writing the formula of each reactant and product. 2. Count the number of atoms of each element on each side of the equation. Make a table if you wish (?) - Metals before nonmetals, then Hydrogen and Oxygen. . 3. Balance the atoms in your table, top to bottom, by adding Stoichiometric Coefficients in front of the reactant or product formulae. The SC multiplies the number of atoms in the formula. 4.1 Writing Balanced Chemical Equations 1. These factors are called Stoichiometric Coefficients in the equation. (We can use them to write the Stoichiometric Ratio for the reaction.) 2. Recount and repeat until balanced. 11 4.1 Chemical Reactions and Chemical Equations In general, balance Metals first, then non-metals, hydrogen and oxygen Note: Hydrocarbons combust to give carbon dioxide and water C 8 H 18 + O 2 CO 2 + H 2 O Examples Al + Fe 2 O 3 Fe + Al 2 O 3 12 We can interpret equations on either a(n) atomic / molecular or molar basis the latter allowing a mass basis (!) 4.1 Chemical Reactions and Chemical Equations 13 4.2 Chemical Equations and Stoichiometry 14 4.2 Chemical Equations and Stoichiometry CH 4( g ) + O 2( g ) CO 2( g ) + H 2 O ( g ) 2 C 8 H 18( l ) + 25 O 2( g ) 16 CO 2(...
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Ch 4 Chemical Reactions HCR BB notes - 1 CHE 1301 Petrucci,...

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