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Understanding Chemical Equations & Balancing for Conservation of Mass

Learn the law of conservation of mass, types of chemical reactions, and balancing equations. Levoisier's contributions and a three-step approach are explored in this comprehensive guide.

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Understanding Chemical Equations & Balancing for Conservation of Mass

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  1. CHEMICAL EQUATIONS LAW OF CONSERVATION OF MASS • BALANCING FOR CONSERVATION OF MASS • TYPES OF CHEMICAL REACTIONS

  2. Levoisier And Balancing Levoisier summarizied his observations of chemical change by stating, among other things, that during a chemical change matter is conserved. • That is, matter is neither created or destroyed. • The mass of the reactants equals the mass of the products.

  3. Comprehension A “balanced” equation has the same number of atoms of each element in both the reactant and product sides of the equation. Reactants Products C + O2 CO2 Two elements make a compound (addition ) Balance: (1) carbon atom (1) carbon atom (2) oxygen atoms (2) oxygen atoms

  4. Consolidation Reactants Products 2H2O 2H2 + O2 a compound makes Two elements (decomposition ) Balance: (4) hydrogen atoms (4) hydrogen atoms (2) oxygen atoms (2) oxygen atoms

  5. A Three Step Approach • First a word equation is written to summarize the reaction in words. hydrogen + oxygen water The above is read as: Hydrogen gas molecules react with oxygen gas molecules to produce water molecules • Then a skeleton equation is written with all the correct formulas for the substances. H2(g) + O2 (g)H2O(l) • Then the equation is balanced for conservation of mass. (Large multipliers are placed in front of substances to balance the equation) • 2H2 + O2 2H2O

  6. Mechanics of Balancing Where do you start? • To start avoid elements which occur more than once on a side. Start with those occurring only once on a side • Pb in PbO2 +HBr-> H2O + PbBr2 + Br2 • Balance complex ions as units rather than individual elements whenever possible. • e.g. NO3, SO4 • Al2(SO4)3+ 3Ba(NO3)2->2Al(NO3)3 +3BaSO4 • Avoid elements which occur by themselves until last. • Be methodical. Don’t jump around balancing a bit here and there.

  7. Types of Chemical Reactions Reactants Products C + O2 CO2 (addition ) two elements make a compound 2 H2O2H2 + O2(decomposition) a compound make two elements AgNO3 + Cu Cu NO3 + Ag (single replacement) compound reacts with element to as metal ions switched places AgNO3 + Cu SO4 Cu NO3 + AgSO4 (double replacement) compound reacts with compound asmetal ions switch places CH4 + 2O2 CO2 + 2H2O (hydrocarbon combustion) hydrocarbon reacts with oxygen to make carbon dioxide and water

  8. Conclusions • The types of chemical reactions can be used to predict possible products given the reactants. • The reaction is then done and the products are observed to verify the prediction. • What evidence would you expect to verify in the following? • AgNO3 + Cu Cu NO3 + Ag (replacement) • __HCl + Mg MgCl2 + H2 (replacement) • Complete this skeleton equation: • CuSO4 + Fe

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