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Chemical Change

Chemical Change. Reactants Products What happens to bonds in a chemical reaction? Broken, form new bonds. Some examples:. Word equations Iron + Oxygen iron (III) oxide (word equation for the rusting of iron)

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Chemical Change

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  1. Chemical Change • Reactants Products • What happens to bonds in a chemical reaction? • Broken, form new bonds

  2. Some examples: • Word equations • Iron + Oxygen iron (III) oxide • (word equation for the rusting of iron) • Hydrogen peroxide water + oxygen • (what happens when you pour this on an open cut? Bubbles of oxygen gas rapidly appear)

  3. Methane + oxygen carbon dioxide + water • (major component of natural gas)

  4. Chemical Equations • Fe(s) + O2(g) Fe2O3(s) • (rusting of iron) • Symbols are used to represent states

  5. Chemical Equations • H2O2(aq) MnO2 H2O(l) + O2(g) • Catalyst: a substance that speeds up the rate of a reaction but that is not used up in the reaction. It is neither a reactant nor a product. It is written above the arrow in an equation because it is not part of the reaction.

  6. Symbols used in chemical equations (see Table)

  7. Review: • Write a skeleton outline for the following chemical reaction (include appropriate symbols): • -solid sodium hydrogen carbonate reacts with hydrochloric acid to produce the aqueous sodium chloride, water, and carbon dioxide gas. • NaHCO3(s) + HCl(aq) NaCl(aq) + H2O(l) +CO2(g)

  8. Review: • sulfur burns in oxygen to form sulfur dioxide • S(s) + O2(g) SO2(g)

  9. Balancing Chemical Equations • Use an example of building a bicycle • 4 components: frames, wheels, handlebars, and pedals • Frame + wheel + handlebar + pedal bicycle (reactants) (product) • (why is this word equation inadequate?) • F + W + H + P FW2HP2 • (this is called an unbalanced equation, in order to balance, the amount of reactants must equal the amount of products)

  10. Balancing Chemical Equations • coefficient: a small whole number that appears in front of a formula in a balanced chemical equation • F + 2W + H + 2P FW2HP2 • Balancing a chemical equation is necessary so that it obeys the law of conservation of mass. • balanced equation: each side of the equation has the same number of atoms of each element

  11. Let’s try a few: • H2(g) + O2(g) H2O(l) • how would you balance this equation?

  12. “Rules for Balancing Equations” • count the number of each atom:hydrogen is balanced but oxygen is not • put a coefficient of 2 in front of H2O, the oxygen is balanced but there are twice as many hydrogen atoms in the product as there are in the reactants • to correct this, put a coefficient of 2 in front of H2 • 2H2(g) + O2(g) 2H2O(l)

  13. Review: • Balance the following equations: • AgNO3 + H2S Ag2S + HNO3 • 2AgNO3 + H2S Ag2S + 2HNO3 • MnO2 + HCl MnCl2 + H2O +Cl2 • MnO2 + 4HCl MnCl2 + 2H2O + Cl2

  14. Demo: Copper(II) chloride with aluminum • Activity: “Balancing Chemical Equations”

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