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Chemical Reactions

This comprehensive guide covers the fundamentals of chemical reactions, including the rearrangement of atoms that leads to the formation of new substances. It details evidence of reactions such as temperature changes, color shifts, and gas production. The document explains the structure of chemical equations, differentiating between reactants and products, and introduces the concept of balancing equations according to the law of conservation of mass. Additionally, it provides practical exercises for writing and balancing skeleton equations.

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Chemical Reactions

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  1. Chemical Reactions • Occur when atoms rearrange – break apart and recombine differently • Produces new substances • Same as a chemical change • Energy is absorbed or released

  2. Evidence of a Rxn • Temperature change • Heat or light • Color change • Odor • Gas bubbles • Appearance of a solid

  3. Rxn Details • Reactants = they react / on left side • Products = they’re produced / on right side • Arrow = yields (new products are formed) • + = separates reactants &/or products • s, g, l, aq = indicates state (or solution)

  4. Ways to Show a Rxn • Word equations: iron(s) + chlorine(g)  iron (III) chloride(s) • Skeleton equations: Fe(s) + Cl2(g)  FeCl3(s) • Balanced chemical equations: 2Fe(s) + 3Cl2 (g)  2FeCl3(s)

  5. 3 Rules of Word Equations • Pure metals (only 1 kind of atom) – will be monoatomic Ex: iron metal = Fe • Pure nonmetals or hydrogen (only 1 kind of atom) – will usually be a gas & will be diatomic unless told otherwise Ex: hydrogen gas = H2

  6. 3 Rules of Word Equations • Compounds (more than 1 kind of atom): A. Will reveal the name Ex: carbon dioxide = CO2 B. Use oxidation numbers to find the correct formula (criss cross & reduce) Ex: magnesium chloride = Mg+2 & Cl-1, so MgCl2

  7. Try It • Write a skeleton equation for these: a. solid barium and oxygen gas react to produce solid barium oxide b. solid iron and aqueous hydrogen sulfate react to produce aqueous iron (III) sulfate and hydrogen gas c. calcium carbonate decomposes to produce calcium oxide and carbon dioxide

  8. Solutions • Ba(s) + O2(g) BaO(s) • Fe(s) + HSO4(aq)  Fe(SO4)3(aq) + H2(g) • CaCO3(s)  CaO(s) + CO2(g)

  9. Chemical Equations • Indicates identities of products & reactants • Indicates relative amounts • Must be balanced (law of conservation of mass) • Balanced with coefficients only • Steps to balance: • Write skeleton (or this will be given to you) • Atom inventory • Guess & check with coefficients • Double check for lowest ratio & equal #

  10. Try It • Decide if the following equations are balanced. If not, balance them. • 2Al + 6HCl  3AlCl3 + 3H2 • C5H12 +11O2  5CO2 + 12H2O • Ba(ClO3) 2  BaCl2 + 2O2

  11. Solutions • 2Al + 6HCl  2AlCl3 + 3H2 • C5H12 +8O2  5CO2 + 6H2O • Ba(ClO3) 2  BaCl2 + 3O2

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