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Unit 2: Chemical Reactions Understanding Chemical Changes

Unit 2: Chemical Reactions Understanding Chemical Changes. LG: I can describe the condition for a chemical reaction to occur and I can represent chemical reactions using word and chemical equations. Recall: Signs of Chemical Change. What clues tell you a chemical reaction has occurred?.

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Unit 2: Chemical Reactions Understanding Chemical Changes

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  1. Unit 2: Chemical ReactionsUnderstanding Chemical Changes LG: I can describe the condition for a chemical reaction to occur and I can represent chemical reactions using word and chemical equations.

  2. Recall: Signs of Chemical Change • What clues tell you a chemical reaction has occurred? Energy Absorbed or Released New Colour Gas Produced Precipitate Formed

  3. Representing Chemical Changes • Example: Cellular respiration is an important process where glucose is broken down by oxygen to produce carbon dioxide and water. Word Equation: Glucose + Oxygen  Carbon Dioxide + Water Chemical Equation: C6H12O6(s) + 6 O2(g) 6 CO2(g) + 6 H2O(l) Reactants Products

  4. Kinetic Molecular Theory • KMT explain the behavior of particles in a substance. • KMT states: • All substances are made of particles that are in constant motion • The particles constantly collide with each other and the surroundings • As temperature increases, particles move faster, increasing the rate of collisions

  5. Collision Reaction Theory • CRT states: • Particles must collide with the correct orientation and sufficient energy to cause a chemical reaction • Correct orientation allows new bonds to form simultaneously • Sufficient energy required to overcome valence shell repulsion • KMT and CRT explain why chemical reactions are affected by factors such as changes in temperature and pressure.

  6. PEOE: Burning Methanol • Question: Will liquid methanol or gaseous methane react faster with oxygen? • PREDICT! • EXPLAIN! • OBSERVE! • EXPLAIN!

  7. Factors Affecting Reaction Rates 1) Temperature – As temperature increases, particles move faster, increasing the frequency and the energy of collisions 2) Concentration – more concentrated substances contain more reactant molecules, increasing the frequency of collisions

  8. Factors Affecting Reaction rates 3) Pressure – decreasing the size of a container, increases the amount of reactant per unit volume, resulting in more frequent collisions 4) Surface Area – When particles are separated from one another, more particles are available to collide with other reactant molecules

  9. Factors Affecting Reaction Rates 5) Nature of Reactants – State reactants (solid, liquid, or gas), and the strength of inter- and intramolecular forces determine how easily they react 6) Catalysts – chemicals that hold reactant molecules in the correct orientation, to reduce the amount of energy required for a reaction; the catalyst itself is not used up in the reaction MnO2 2 H2O2 2 H2O + O2

  10. Factors Affecting Reactions Rates • http://www.youtube.com/watch?v=OttRV5ykP7A

  11. Homework! • Complete Handout & attempt to balance equations in #5

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