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CHEMISTRY

CHEMISTRY. Balancing Equations. The law of Conservation of Matter. Matter is neither created nor destroyed, but conserved. Chemical Reaction. When a chemical reaction occurs what are some evidences that a new substance has been produced? Color Change Production of a gas

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CHEMISTRY

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  1. CHEMISTRY Balancing Equations

  2. The law of Conservation of Matter • Matter is neither created nor destroyed, but conserved.

  3. Chemical Reaction • When a chemical reaction occurs what are some evidences that a new substance has been produced? • Color Change • Production of a gas • Formation of a precipitate • Change in Temperature • Explosion

  4. Chemical Equations • Chemical equations are a way to illustrate what happens during a chemical reaction. • Reactants Products • Example • Zinc metal reacts with hydrochloric acid to produce zinc chloride and hydrogen gas. • This does not show the law of conservation or the ratio that occurs when this chemical change takes place. • We need an easier way.

  5. Getting Started • Word Equation: • Zinc + Hydrochloric Acid Zinc Chloride + Hydrogen • Symbol Equation: Formulas must be correct • Zn + HCl ZnCl2 + H2 • This shows a mass deficiency • Zn HCl Zn Cl2 H2 • 65.4g/mol + ( 1.01 + 35.5 ) = 65.4 + 2[ ( 35.5 )] + 2 ( 1.01 ) • 102 g/mol ≠ 140 g/mol • What must be done if the law of conservation is to be met?

  6. Continue + + Zn HCl ZnCl2 H2 • On the reactant side On the product side • 1 Zn and 1 H and 1 Cl One Zn and 2 Cl and 2 H This is illustrating the creation of matter which goes against the Law of conservation. How should we correct the problem?

  7. Continue + + Zn 2HCl ZnCl2 H2 The number of molecules of HCl is represented by the Coefficient of 2. Thus satisfying the Law of Conservation

  8. Let’s Practice • Consider the reaction: • Ammonia reacts with oxygen to produce nitrogen dioxide and water. • SKELITON EQUATION • NH3 + O2 NO2 + H2O • Balance the hydrogen first ( Note: water can not have an odd coefficient because of the O2 )

  9. More • NH3 + O2 NO2 + H2O • There are three hydrogen’s on the left and two on the right, but a 3 coefficient won’t work because water will have an odd number, so double the 3 to a 6. Add a 4 to the ammonia and that gives you 12 hydrogen on both sides. • 4 NH3 + O2 NO2 + 6 H2O • Next balance the nitrogen. • 4 NH3 + O2 4 NO2 + 6 H2O • This gives you 4 nitrogen on both sides of the equation. • Next balance the oxygen • 4NH3 + 7 O2 4 NO2 + 6 H2O • This is the ratio these substances will react.

  10. Ionic Reactions • When a substance dissolves in water it dissociates into positive and negative ions where the opposite charges balance. • MgCl2 ------> Mg+2 + 2Cl-1 • +2 + 2(-1) = 0

  11. Rules for SolubilityPage 218 • 1. Nitrates are soluble. • 2. Elements of group one and NH4+1 (ammonium) are soluble. • 3. All chlorides are soluble except Ag, Hg, and Pb. • 4. All sulfates are soluble except Ba, Pb, and Ca. • 5. Most hydroxides are insoluble except group one elements. • 6. Most sulfides, carbonates, and phosphates are slightly soluble. • Precipitates are formed when two soluble ions are mixed to form an insoluble substance. • AgNO3 ---- > Ag+1 + NO3-1 Rule 1 • HCl ---- > H+1 + Cl-1 Rule 3 • Ag+1 + Cl-1 ---- > AgCl (ppt) Rule 3

  12. Types of Reactions • Acid – Base Reactions ( Neutralization ) • Oxidation – Reduction Reactions ( Redox ) • Single Displacement Reactions ( SD ) • Double Displacement Reactions ( DD ) • Direct Combination Reactions ( DC ) • Decomposition Reactions ( DEC ) • Combustion Reactions ( C )

  13. Acid – Base Reactions • Acid : A proton donor ( Hydrogen is a proton when it loses an electron because it has no neutron. ) All acids contain hydrogen. • HCl ---> H+1 + Cl-1 hydrochloric acid • H2SO4 --- > H+1 + HSO4-1 sulfuric acid • Base : A proton acceptor ( All bases contain the hydroxide ion OH-1) • NaOH ------ > Na+1 + OH-1 sodium hydroxide • Mg(OH)2 ----- > Mg+2 + 2OH-1 magnesium hydroxide

  14. Neutralization • H2SO4 + 2 NaOH --- > Na2SO4 + 2H2O • Acid + Base --- > Salt + water • Salt: Metal with the negative part of an acid is defined as a salt.

  15. Oxidation - Reduction • Oxidation: Loss of electrons and a gain in positive charge or a decrease of the negative charge. • Reduction: Gain of electrons and a decrease in the positive charge or an increase in the negative charge • Ag --- > Ag+1 + 1e- Oxidation • Mg+2 + 2e- --- > Mg Reduction • In an oxidation – reduction reaction the number of electrons gained is equal to the number of electrons lost.

  16. Redox • An example of a Redox Reaction is found in the following example: • KMnO4 + HCl --- > KCl + MnO2 + Cl2 + H2O • Find the Oxidation Number for each element • K+1Mn+7O4-2 + H+1Cl-1 --- > K+1Cl-1 + Mn+4O2-2 + Cl20 + H2+1O-2 Gain of 3 electrons - Reduction Loss of 1 electron - oxidation ( Mn+7 + 3e- --- > Mn+4 ) 2 = 2Mn+7 + 6e- --- > 2Mn+4 ( 2Cl-1 --- > Cl2 + 2e- ) 3 = 6Cl-1 --- > 3Cl2 + 6e- • 2 KMnO4 + 8 HCl --- > 2 KCl + 2 MnO2 + 3 Cl2 + 4 H2O

  17. Single Displacement ( SD ) • Single displacement occurs when one element displaces another element in a compound. Usually the positive elements. • Element 1 + Compound 2 --- > Compound 1 + Element 2 • Zn + HNO3 --- > Zn( NO3 )2 + H2 • Balance the equation • Zn + 2 HNO3 --- > Zn( NO3 )2 + H2 • The zinc replaced the hydrogen and bonded to the nitrate. • NOTE: Positive elements replace positive elements

  18. Double Displacement • Double displacement occurs when two positive elements or PAI change places with the negative counterpart. • Compound + Compound --- > Compound + Compound • AB + CD ---- > AD + CB • CaCl2 + Al( NO3)3 --- > Ca( NO3)2 + AlCl3 • Balance the equations • 3CaCl2 + 2 Al( NO3)3 --- > 3Ca( NO3)2 + 2AlCl3

  19. Direct Combination • Direct combination occurs when two elements, two compounds, or an element and a compound combine to form only one new compound. • 4Li + O2 --- > 2 Li2O : Element + Element -- > Compound • 2KCl + 3O2 --- > 2KClO3 : Element +Compound -- > Compound • NH3 + HCl --- > NH4Cl : Compound +Compound -- > Compound

  20. Combustion • In a combustion reactions, oxygen is always a reactant and water is always a product. • C5H12 + 8O2 --- > 5CO2 + 6H2O • 4NH3 + 7O2 --- > 4NO2 + 6H2O • In Combustion reactions energy is always released.

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