Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 3: Sections 1 to 3.
3.1: Chemical Equations Because atoms are unbreakable for the purposes of chemical reactions, we must of reactions as involving the rearrangements of whole atoms or groups of atoms. Because mass is conserved, no atoms are ever created or destroyed in a chemical reaction, so the number of each elemental type of whole atoms must be the same before and after the reaction occurs. This allows us to determine the actual number of atoms involved from partial information.
3.2: Balancing Chemical Equations The first step of balancing a reaction is to determine which chemicals are involved. Then we adjust coefficients (the number of whole atoms or molecules in a unit), Study the process on p. 152 carefully. We leave until last balancing the one element that stands alone, since that piece we can manipulate without affecting anything else. For combustion reactions, this is the oxygen.
3.3: Chemical Equilibrium. Chemical reactions occur between individual molecules. The amount of energy available at the point of a reaction determines which set of molecules breaks open to rearrage atoms in a different set. At any given moment, rearrangements may proceed in both directions. The overall effect depends on how many reactions occur in each direction. If most reactions at the moleuclar level favor production of a particular set of molecules, we consider these the products of the overall reaction and say the reaction is product-favored. If we start with one set of molecules and only a few react to form new sets, we say the reaction is reactant-favored.
|1||Write out the reaction|
|Methane and oxygen react to form water and carbon dioxide.|
|2||Substitute formulae for|
reactants and products
|CH4 + O2 → CO2 + H2O|
|3||Since O2 is by itself, leave it until last. Balance carbon first.||There is one C in products, one in reactants; carbon is balanced.|
|4||Next balance hydrogen||There are four hydrogens in CH4; we need two water molecules so that we will have four hydrogen atoms in the products:|
CH4 + O2 → CO2 + 2H2O
|5||Now balance oxygen.||There are three oxygens in the products, so we need 3/2 diatomic oxygen for each methan molecule:|
CH4 + 3/2 O2 → CO2 + 2H2O
|6||Double the reaction to get rid of the fraction, if desired||2CH4 + 3O2 → 2CO2 + 4H2O|
|7||Verify counts in reactants and products||Carbon: 2|
|8||Declare victory!||Equation is balanced/|
Read the following weblecture before chat: Chemical Reactions
Review the Videos at Thinkwell Video Lessons under REACTIONS IN AQUEOUS SOLUTIONS.
References: Illustrated Guide to Home Chemistry Experiments [Required text], or Home School Chemistry Kit Manual which comes with the Home Scientist Chemistry Kit CK101 set and is available online at The Home Scientist.
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