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Chapter 4 : CHEMICAL REACTIONS Reactants: Zn + I2 Product: Zn I2 Feb. 17, 2006 Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O2(g) → 2 Al2O3(s) The numbers in front are called stoichiometric coefficients The letters (s), (g), and (l) are the physical states of compounds (solid, liquid or gas). Feb. 17, 2006 1 Chemical Equations 4 Al(s) + 3 O2(g) → 2 Al2O3(s) This equation means 4 Al atoms + 3 O2 molecules give→ 2 molecules of Al2O3 4 moles of Al + 3 moles of O2 give→ 2 moles of Al2O3 Feb. 17, 2006 Chemical Equations • Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change. • This is the Law of the Conservation of Matter Screen 4.3 on CD-ROM Feb. 17, 2006 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. 2 Al(s) + ___ 3 Br2(liq) →___ 1 Al2Br6(s) ___ Feb. 17, 2006 Balancing Equations 5 O2(g) 1 3H8(g) + _____ ____C 3 4 _____CO 2(g) + _____ H2O(g) 11 O2(g) 2 B4H10(g) + _____ ____ 4 B2O3(g) + _____ 10 H2O(g) _____ Feb. 17, 2006 3