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Understanding Chemical Reactions and Balancing Equations

Dive into the essentials of chemical reactions with a focus on the law of conservation of matter. We examine various types of chemical changes—evidencing new substances through color changes, gas production, temperature shifts, and more. Learn how to balance chemical equations effectively through practical examples, such as the reactions of zinc with hydrochloric acid and ammonia with oxygen. This guide also covers the principles of ionic reactions, solubility rules, and different reaction types, including redox and neutralization processes.

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Understanding Chemical Reactions and Balancing Equations

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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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