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Chemical Equations

Chemical Equations. Because the same atoms are present in a reaction at the beginning ( reactants ) and at the end ( products ), the amount of matter in a system does not change. The Law of Conservation of Matter. 20%. Chemical Factory. 100%. 100%. 80%. Kotz web.

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Chemical Equations

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  1. Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. The Law of Conservation of Matter 20% Chemical Factory 100% 100% 80% Kotz web

  2. Chemical Equations Because of the principle of the conservation of matter, An equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788

  3. Cl H H H Cl Cl Cl H reactants products reactants products H H Cl Cl Unbalanced and Balanced Equations H Cl Cl Cl H H H2 + Cl2 2 HCl (balanced) (unbalanced) H2 + Cl2 HCl 2 1 2 2 1 2 2 2

  4. Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. 2 Na + H2O  2 NaOH + H2 2 Na + 2 H2O  2 NaOH + H2

  5. Balancing Chemical Equations Example NO(g) + O2(g)  NO2(g) • is it balanced? • 2NO(g) + O2(g)  2NO2(g)

  6. Balancing Chemical Equations An important point to remember • 2NO(g) + O2(g)  2NO2(g) • The 2 to the left of NO(g) and NO2(g) refers to the number of molecules present in the balanced equation. • It is a “multiplier” for every atom in the molecule. The subscript 2 in O2 (g) and NO2(g) refers to the number of atoms of this type that are present in each molecules (or ionic compound).

  7. Write a balanced equation for the reactions Cl2 + NaBr  Br2 + NaCl Cl2 + 2 NaBr  Br2 + 2 NaCl Al2(SO4)3 + CaCl2 CaSO4 + AlCl3 Al2(SO4)3 + 3 CaCl2 3 CaSO4 + 2 AlCl3

  8. CH4 + 2 O2 CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

  9. Reactants  Products + C(s) + O2(g) CO2(g) carbon oxygen carbon dioxide Reactants Product 1 carbon atom 1 carbon atom 2 oxygen atoms 2 oxygen atoms catalyst – speeds up reaction + Pt 2 H2(g) + O2(g) H2O(l) hydrogen oxygen water 2 Pt Reactants Product 2 hydrogen atoms 2 hydrogen atoms 2 oxygen atoms 1 oxygen atoms Reactants Product 2 hydrogen atoms 4 hydrogen atoms 2 oxygen atoms 2 oxygen atoms Reactants Product 4 hydrogen atoms 4 hydrogen atoms 2 oxygen atoms 2 oxygen atoms Un balanced

  10. CO2 + H2O C6H12O6 + O2 H2 + O2 H2O Na + Cl2NaCl Photosynthesis 6 6 6 Formation of water 2 2 Formation of salt 2 2

  11. H2O2 H2O + O2 electricity H2O H2 +O2 NI3N2 + I2 Hydrogen Peroxide 2 2 Electrolysis of water 2 2 Nitrogen triiodide 2 3

  12. Exercise: Balance & represent these chemical reactions. 1. Sb + Cl2 SbCl3 2. Mg + O2 MgO 3. CaCl2 Ca + Cl2 4. NaClO3 NaCl + 3 O2 5. Fe + HCl FeCl2 + H2 6. CuO + H2 Cu + H2O 7. Al + H2SO4 Al2(SO4)3 + H2

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