Science

• Chemical Reactions


  The process of converting one set of chemical substances (the reactants) to another set of substances (the products)
• Chemical reactions happen absolutely everywhere
• Chemical reactions can be much less controlled than in the lab, sometimes far messier, and they generally occur whether you want them to or not
• Examples of chemical reactions


  • Fire raging across a forest
  • Iron rusting in the presence of oxygen and water over a period of years
  • Fruit ripening on a tree
• Chemical reactions are important in many professions
• Professions where chemical reactions are important

  • Dieticians
  • Chemical engineers
  • Chemists
• Laws of Chemical Change


  Generalizations that should hold true when substances undergo chemical reactions
• Law of Conservation of Mass


  The mass of the system (total amount of "stuff" present) does not change during a chemical reaction
• Antoine Lavoisier


  • Performed many quantitative experiments and observed that the mass of the system does not change during a chemical reaction
  • Proposed that substances are neither created nor destroyed, but rather, changed form during reactions
• Law of Definite Composition

  The ratio in which the reactants are consumed is always constant, regardless of the starting amounts
• Joseph Proust


  • Performed dozens of chemical reactions and observed the constant ratio of reactants consumed
  • Formulated the law of constant composition (law of definite proportions)
• Law of Multiple Proportion


  It is possible for two elements to form more than one compound, but whatever the compound is, it will always contain elements combined in whole number ratios
• John Dalton


  • Proposed that matter was made of atoms of unique substances that could not be created or destroyed
  • Recognized the law of multiple proportions and helped cement Lavoisier's observations
• Evidence of chemical reactions

  • Change in odor
  • Change in color
  • Evolution of gas
  • Formation of precipitate (insoluble particles)
  • Evolution of light and heat
  • Change in temperature or energy
  • Change in form
• Chemical Equation


  The symbolic representation of a chemical reaction, with reactants on the left and products on the right

  
• The Law of Conservation of Mass says that atoms are neither created nor destroyed during any chemical reaction
• Coefficients


  The whole numbers written in front of the symbols or formula, representing the number of atoms
• Steps to balance a chemical equation

  1. Determine the correct formula for all the reactants and products

  2. Find out which atoms are unbalanced and balance each element at a time by placing a coefficient

  3. Balance the Hydrogen and Oxygen last

  4. Balance the groups of atoms acting as a unit like polyatomic ions

  5. Adjust the coefficients of the monoatomic elements last

  6. Check that the final balanced equation has coefficients in the lowest possible whole number
• Balanced chemical equations


  • 2Al + 3Cl2 → 2AlCl3
  • 3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O
  • H2SO4 + 2NaOH → 2H2O + Na2SO4