Chemical Reactions

1
Chapter 4.1

• Chemical Reactions

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Chemical Reactions

• Chemical Change the transformation of one or
  more substances into different substances with
  different properties

3
Demonstrations

• Lycopodium oxygen in the presence of heat
• Iron (III) chloride (0.2M) Sodium hydroxide (1M)
• Lead (II) nitrate potassium iodide
• Magnesium metal hydrochloric acid (1M) also
  try hydrogen gas test
• Urea water

4
Clues to a chemical change

• Change in colour
• Energy is released or absorbed
• Gas is produced
• A precipitate (solid) forms from two liquids
• Difficult to reverse
• NOTE a change in state or dissolving a substance
  is NOT a chemical change

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How can we speed up a reaction?

• http//www.youtube.com/watch?vOttRV5ykP7Asnsem
• In order for a reaction to occur, reactants must
  collide in the correct orientation and with the
  correct amount of energy

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Methods of increasing speed

1. Decrease the volume of the reaction vessel
2. Increasing concentration
3. Increase temperature
4. Increase surface area
5. Add a catalyst (this decreases the amount of
   energy needed for a reaction to occur but doesnt
   get consumed in the reaction)

increases the number of collisions
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Chemical Equations

• Represent chemical reactions by using words or
  symbols and formulas
• Starting materials are called reactants
• New substances are called products
• An arrrow (?) is read as produces
• States of matter appear in brackets (s)solid
  (l)liquid (g)gas (aq) dissolved in water

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Word Equations

• Use words to represent reactions
• Use all of your naming rules to do this!
• Ex.
• Magnesium Hydrochloric acid ? Magnesium
  chloride Hydrogen gas
• Copper (II) sulfate Ammonium chloride ? Copper
  (II) chloride Ammonium sulfate
• Sodium metal oxygen gas ? sodium oxide

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Skeleton Equation

• An unbalanced equation that shows all reactants
  and products in a chemical reaction written as
  formulas
• Rules
• -write the symbol of a metal element that is NOT
  in a compound ex. Iron Nail is Fe

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Skeleton Equations

• -If the non-metal is part of Hockey stick and
  puck, write it as a diatomic molecule
• H2, N2, O2, F2, Cl2, Br2, I2
• Ex. Oxygen gas reacts with fluorine gas
• O2 F2
• - Write the formula of any other compound using
  the rules you have learned

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Law of Conservation of Mass

• States that in a chemical reaction, the mass of
  the products ALWAYS EQUALS the mass of the
  reactants since elements cannot be created or
  destroyed in a chemical reaction, they can only
  be rearranged!

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Formula Equations

• Notice states of matter are always included
• Coefficients are used to show the ratios of the
  different substances present in the reaction
  (follows the law of conservation of mass)
• Ex.
• Mg (s) 2HCl (aq) ? MgCl2 (aq) H2 (g)

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Balancing

• Balance polyatomic ions first if the same ion
  appears on both sides of the equation
• Balance all other elements except H and O
• Balance H
• Balance O

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Examples

• Balance the following chemical equations.
• 1. Fe H2S04 ? Fe2(SO4)3
  H2
• 2. C2H6 O2 ? H2O CO2
• 3. KOH H3PO4 ? K3PO4 H2O
• 4. SnO2 H2 ? Sn H2O

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Homework

• p. 155 3,5
• worksheet