unit 2: chemical reactions understanding chemical changes
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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?. - PowerPoint PPT PresentationTRANSCRIPT
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.
Recall: Signs of Chemical Change• What clues tell you a chemical reaction
has occurred?
Gas Produced
Energy Absorbed or Released
Precipitate Formed
New Colour
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
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
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.
PEOE: Burning Methanol• Question: Will liquid methanol or gaseous
methane react faster with oxygen?– PREDICT!– EXPLAIN!– OBSERVE!– EXPLAIN!
Factors Affecting Reaction Rates1) 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
Factors Affecting Reaction rates3) 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
Factors Affecting Reaction Rates5) 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
2 H2O2 2 H2O + O2
MnO2
Factors Affecting Reactions Rates
• http://www.youtube.com/watch?v=OttRV5ykP7A
Homework!• Complete Handout & attempt to balance
equations in #5