Chemical Equations

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Chemical Equations
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Vocabulary!

• Coefficient
• is a small, whole number that appears IN FRONT
• of a chemical formula in a chemical equation.
• Example 4 HCl
• Word Equation
• an equation in which the reactants and products
  in a chemical reaction are represented by words.
• Example hydrogen oxygen yields water
• Formula Equation
• represents the reactants and products of a
  chemical reaction by their symbols or formulas.
• Example 2 H2 O2 ? 2 H2O

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Why Balance?

• The coefficients of a chemical reaction indicate
  relative amounts of reactants and products.
• Example H2(g) Cl2(g) ? 2HCl(g)
• The relative masses of the reactants and products
  can also be determined from the coefficients.
• The reverse reaction for a chemical equation has
  the same relative amounts of substances as the
  forward reaction.
• So what?
• Because of this, chemical reactions can be read
  in any direction. Forward and Reverse.

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Law of Conservation of Mass

• The law of conservation of mass states that
  matter is neither lost nor gained in chemical
  reactions. It simply changes form.

Watch Me!
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Rules for Balancing Equations

• Write a word equation. Determine the reactants,
  the products, and the physical states involved.
• Translate to Chemistry. Write the unbalanced
  equation that summarizes the reaction described
  in Step 1, using chemical formulas for names.

• Solid zinc and hydrochloric acid react to yield
  zinc chloride and hydrogen gas.
• Zn(s) HCl ? ZnCl2 H2(g)

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Rules for Balancing Equations

• Satisfy the law of conservation of mass.
• Start with the most complicated molecule.
  Determine the coefficients necessary
• to satisfy the law of conservation of mass.
• Check your work.

• 3. Zn(s) HCl ? ZnCl2 H2(g)
• __Zn(s) __HCl ? 1 ZnCl2 __H2(g)
• 1 Zn(s) 2 HCl ? 1 ZnCl2 __H2(g)
• 1 Zn(s) 2 HCl ? 1 ZnCl2 1 H2(g)
• 4. 1 Zn, 2 H, 2 Cl ? 1 Zn, 2 H, 2 Cl

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Examples

• __Al __O2 ? __Al2O2
• __C2H6 __O2 ? __CO2 __H2O
• __Fe2O3 __H2SO4 ? __Fe2(SO4)3 __H2O