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Calculating Chemical Equations

Calculating Chemical Equations. Why and How Many Atoms Bond. Chemical Equations. A shorthand way to describe a chemical reaction using chemical symbols and formulæ. Chemical Equations. Has three parts Reactants Substances present before the reaction Products

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Calculating Chemical Equations

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  1. Calculating Chemical Equations Why and How Many Atoms Bond

  2. Chemical Equations • A shorthand way to describe a chemical reaction using chemical symbols and formulæ

  3. Chemical Equations • Has three parts • Reactants • Substances present before the reaction • Products • Substances present after the reaction • Yield Arrow • Indicates the direction of a reaction • Some reactions are reversible

  4. Writing a Chemical Equation Chemical symbols give a “before-and-after” picture of a chemical reaction Reactants Products MgO + C CO + Mg magnesium oxide to form carbon monoxide reacts with carbon and magnesium

  5. Balancing Chemical Equations • Equations must be balanced to observe the Law of Conservation of Matter • Matter can not be created or destroyed under normal reactions • If you begin a reaction with 5 g of Hydrogen, you must end up with 5 g of Hydrogen

  6. A Balanced Chemical Equation Same numbers of each type of atom on each side of the equation Al + S Al2S3 Not Balanced 2Al + 3S Al2S3Balanced

  7. Balancing Chemical Equations • Count atoms on both sides of the yield arrow • Determine which elements are unequal • Use coefficients to balance the number of atoms on both sides • If you multiply one element in a compound, you multiply both elements in a compound • You can treat Polyatomic Ions as one if they appear on both sides of the equation • Go for the highest unequal elements first • Leave solitary elements for last

  8. Steps in Balancing An Equation Fe3O4 + H2 Fe +H2O Fe:Fe3O4 + H23 Fe +H2O O:Fe3O4 + H2 3 Fe +4H2O H: Fe3O4 + 4 H2 3 Fe +4H2O

  9. Balancing Chemical Equations Mg + N2 Mg3N2 Al + Cl2 AlCl3

  10. Balancing Chemical Equations Fe2O3 + C Fe + CO2 Al + FeO Fe + Al2O3 Al + H2SO4 Al2(SO4)3 + H2

  11. Types of Chemical Reactions • Synthesis • Two or more substances form one new substance H2 + O2  H2O N2 + H2  NH3

  12. Types of Chemical Reactions • Decomposition • One substance breaks down to form two or more new substances PbCO3  PbO + CO2 H2CO3  H2O + CO2

  13. Types of Chemical Reactions • Single Displacement • One substance replaces another in a compound Li + AlCl3  LiCl + Al

  14. Types of Chemical Reactions • Double Displacement • Two substances “swap partners” in two compounds KOH + HBr  KBr + H2O NaOH + H2CO3  Na2CO3 + H2O

  15. Types of Chemical Reactions • Neutralization • Double-displacement reaction where an acid and a base form a salt and water KOH + HBr  KBr + H2O NaOH + H2CO3  Na2CO3 + H2O

  16. Acids and Bases • Acids • Taste Sour • Have a pH of less than 7 • Produce Hydronium H3O+1 in solution • Have an “extra” H- on the beginning of the formula H2SO4 – (Hydro)Sulfuric Acid H3PO4 – (Hydro)Phosphoric Acid HNO3 – (Hydro)Nitric Acid HCl – Hydrochloric Acid

  17. Acids and Bases • Bases • Taste bitter • Have a pH of more than 7 • Produce Hydroxide OH–1 in solution • Have an –OH on the end of the formula NaOH – Sodium Hydroxide KOH – Potassium Hydroxide Ca(OH)2 – Calcium Hydroxide NH4OH– Ammonium Hydroxide

  18. The Litmus Test • Using an indicator can tell whether a substance is acidic or alkaline • Litmus paper is a frequently-used indicator • Acids turn BLUE litmus paper RED • Bases turn RED litmus paper BLUE

  19. Types of Chemical Reactions • Combustion • Where a carbon compound combusts with oxygen gas to form carbon dioxide and water CH4 + O2  CO2 + H2O C2H6 + O2  CO2 + H2O

  20. Let’s get it started • Some reactions require a little “jump start” to proceed • Activation Energy • Energy required to be applied to start a reaction • Examples • Applying friction to start a match • The match causing a log to burn

  21. Change in ENERGY • Every reaction has some change in energy • Two possibilities:

  22. Endothermic – absorbs energy from the environment to complete reaction • Feels “COLD” to its surroundings • Products have MORE energy than the reactants

  23. Exothermic – releases energy to the environment as the reaction proceeds • Feels “HOT” to its surroundings • Products have LESS energy than reactants

  24. Speeding Up • A Catalyst is a chemical that participates in a chemical reaction without being changed by the reaction • Catalysts speed up reaction rates by • acting as a “convenience” • lowering the activation energy • Organic catalysts are called ENZYMES

  25. Hungry? • Without enzymes, your cells would NEVER keep up with the energy demands

  26. Slowing Down • An Inhibitor also participates in a chemical reaction without being changed by the reaction • Inhibitors slow down reaction rates by • acting as an “inconvenience” • raising the activation energy

  27. Normal reaction / normal activation energy With a catalyst / lower activation energy

  28. Counting Atoms Subscripts Coefficients Diatomic Molecules Polyatomic Ions Parenthesis Oxidation Numbers Binary Formulæ Criss-cross method Naming Rules Ionic Roman Numerals Covalent Prefixes Balancing Equations NEVER change subscripts Law of Conservation of Matter Types of Reactions Changes in Energy during reactions

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