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Lecture 11.1- Balancing Equations

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Section 11.1 lecture for Honors & Prep Chemistry

Section 11.1 lecture for Honors & Prep Chemistry

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  • Three common chemical reactions are shown. a) When methane gas burns, it combines with oxygen to form carbon dioxide and water. b) Iron turns to red-brown rust (iron(III) oxide) in the presence of oxygen in the air. c) Hydrogen peroxide decomposes to water and oxygen when used as an antiseptic.
  • Hydrogen peroxide decomposes to form water and oxygen gas. a) Bubbles of oxygen appear slowly as decomposition proceeds. b) With the addition of the catalyst manganese(IV) oxide (MnO 2 ), decomposition speeds up. The white “smoke” is condensed water vapor.
  • Three common chemical reactions are shown. a) When methane gas burns, it combines with oxygen to form carbon dioxide and water. b) Iron turns to red-brown rust (iron(III) oxide) in the presence of oxygen in the air. c) Hydrogen peroxide decomposes to water and oxygen when used as an antiseptic.
  • Three common chemical reactions are shown. a) When methane gas burns, it combines with oxygen to form carbon dioxide and water. b) Iron turns to red-brown rust (iron(III) oxide) in the presence of oxygen in the air. c) Hydrogen peroxide decomposes to water and oxygen when used as an antiseptic.
  • Conceptual Problem 11-3

Lecture 11.1- Balancing Equations Lecture 11.1- Balancing Equations Presentation Transcript

  • Describing Chemical Reactions
    • On May 6, 1937, the huge airship Hindenburg erupted into a fireball.
    • Within a short time, 210,000 cubic meters of hydrogen had burned and the airship was destroyed.
    • The chemical reaction that
    • occurred is
    • “ hydrogen combines with
    • oxygen to produce water.”
    • Basic chemical equation format
    • Reactants  Products
    yields
      • Word Equations use chemical names
    bleach + ammonia  poisonous gas
          • write the formulas of the reactants to the left of the yields sign (arrow) and the formulas of the products to the right.
      • To write a chemical equation
          • H 2 + O 2  H 2 O
    Reactants Product
          • An unbalanced(skeleton) equation does not indicate the relative amounts of the reactants and products.
          • Here is the unbalanced equation for rusting:
          • Fe + O 2  Fe 2 O 3
    Why is it unbalanced?
        • Methane + Oxygen  Carbon dioxide + Water
    CH 4 + O 2  CO 2 + H 2 O
        • A catalyst is a substance that speeds up the reaction but is not used up in the reaction.
        • Without Catalyst With Catalyst
    • Special conditions, including use of a catalyst, are written above the arrow
    • H 2 O 2 H 2 O + O 2
    KI
  • Writing Chemical Equations
    • Complete chemical equations show the state of matter (in parenthesis) after each formula.
          • NaCl ( s )
          • H 2 O ( l )
          • O 2 ( g )
        • iron + oxygen  iron(III) oxide
    Fe (s) + O 2 (g)  Fe 2 O 3 (s)
        • Hydrogen Peroxide  Water and Oxygen
    H 2 O 2 (aq)  H 2 O (l) + O 2 (g)
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      • Chemical equations are not complete unless they are BALANCED.
      • To write a balanced equation add the coefficients that will show the reaction obeying the law of conservation of mass.
    PRODUCTS REACTANTS
        • Coefficients are small whole numbers that are placed in front of the formulas in an equation in order to balance it.
    2H 2 + O 2  2H 2 O NEVER change subscripts subscripts coefficient
  • NEVER change subscripts subscripts coefficients
        • In a balanced equation each side of the equation has the same number of atoms of each element and mass is conserved.
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      • 1. Propane gas reacts with oxygen to produce water vapor and carbon dioxide. Choose the correct word equation for this reaction.
        • propane + carbon dioxide  water + oxygen
        • propane + oxygen + water  carbon dioxide
        • propane + oxygen + water + carbon dioxide
        • propane + oxygen  water + carbon dioxide
      • 2. What coefficient for H 2 SO 4 is required to balance the following equation?
      • Ca 3 (PO 4 ) 2 + ____ H 2 SO 4  3CaSO 4 + 2H 3 PO 4
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