Chemical Reactions Factors Affecting Rates of Reaction January 9, 2015.
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Transcript of Chemical Reactions Factors Affecting Rates of Reaction January 9, 2015.
Chemical Reactions
Factors Affecting Rates of Reaction
January 9, 2015
WARM-UP: Identify the type of reaction below:
a. 2 Na + Cl2 2 NaCl
b.Zn + 2 HCl ZnCl2 + H2
c. PbO2 Pb + O2
d.2 H3PO4 + 3 Ca(OH)2 Ca3(PO4)2 + H2O
e. CaCl2 + 2AgNO3 Ca(NO3)2 + 2AgCl
f. CH4 + 2 O2 CO2 + 2 H20
SYNTHESIS
S.R.
DECOMP
D.R.
D.R.COMB.
Collision Theory• Molecules must…
• Collide with each other hard enough to react
• Be in a favorable orientation
• In a successful collision, existing bonds are broken and new bonds formed while reactants become products
Collision Theory Con’t• REACTION RATE:
• Informally, reaction rate is the speed at which a chemical reaction takes place
• Formally, the reaction rate is the change in concentration of reactants or products over time
Factors that Affect Reaction Rates• 1. TEMPERATURE:
• Increasing temperature means the particles move faster
• Particles collide more frequently and with more energy
• Reactions occur faster
Factors that Affect Reaction Rates• 2. CONCENTRATION:
• Increasing concentration means the molecules are closer together
• Particles collide more frequently
• Reactions occur faster
Factors that Affect Reaction Rates• 3. PARTICLE SIZE:
• Molecules can only collide on the surface
• Smaller particles have a larger surface area
• Reactions occur faster• Dissolving speeds up a reaction
• Smallest particles are molecules or ions
Factors that Affect Reaction Rates• 4. CATALYSTS:
• A catalyst is a substance that speeds up a reaction without being used up • Example: enzymes
• Increases the number of collisions
• Reduces the activation energy• The minimum energy
needed for a reaction to occur
• Activation Energy: the minimum amount of energy required to make a reaction proceed forward• Catalysts speed up reactions by lowering
activation energy
Activation Energy
Check for Understanding
1. According to “Collision Theory”, what two conditions must be fulfilled for a reaction to occur?
2. How does increasing temp cause the reaction to occur faster?
3. Which has a larger surface area, a single stick of butter or butter cubed into small pieces? Which would cause a reaction proceed faster?
4. What is the activation energy?
Check for Understanding ANSWERS
1. The molecules must collide with enough strength to react and be in a favorable orientation
2. It speeds up the molecules and they collide more frequently
3. Cubed butter because it is smaller in size; cubed butter will react faster
4. Minimum amount of energy required for a reaction to occur
Reaction rate can be stated as:
1. The decrease in the concentration of reactants with time
or
2. The increase in the concentration of products with time
Reaction Rate
• In the reaction: A --> B
1. A is the reactant and B is the product
2. Notice that the concentration of A decreases over time and B increases
REACTANTS:Minimum # moles at 60 minMaximum # moles at 0 min
PRODUCTS:Minimum # moles at 0 minMaximum # moles at 60 min
EQUILIBRIUM:Approximately 24 min (both reactants and products have 0.5 moles)
REACTION RATE
En
erg
y
Reaction coordinate
Reactants
Products
Ene
rgy
Reaction coordinate
Reactants
Products
Activation Energy: Minimum energy to make the reaction happen
Ene
rgy
Reaction coordinate
Reactants
Products
Activated Complex or Transition State
Ene
rgy
Reaction coordinate
Reactants
Products
Overall energy change
An Endothermic Reaction (Energy Absorbed)
Ene
rgy
Reactants Products®
CaCO3 (s)
CaO (s) + CO2 (g)
+176 kJ
An Exothermic Reaction (Energy Released)
Ene
rgy
Reactants Products®
C + O2
CO2
-395 kJ
Ene
rgy
Reaction coordinate
Reactants
Products
Activation Energy - Minimum energy to make the reaction happen
Ene
rgy
Reaction coordinate
Reactants
Products
Activation Energy - Minimum energy to make the reaction happen
Activated Complex or Transition State
PE of the Reactants
Ene
rgy
Reaction coordinate
Reactants
Products
Activation Energy - Minimum energy to make the reaction happen
Activated Complex or Transition State
PE of the Reactants
PE of the Activated Complex
Ene
rgy
Reaction coordinate
Reactants
Products
Activation Energy - Minimum energy to make the reaction happen
Activated Complex or Transition State
PE of the Reactants
PE of the Activated Complex
PE of Products
Ene
rgy
Reaction coordinate
Reactants
Products
Activation Energy - Minimum energy to make the reaction happen
Activated Complex or Transition State
PE of the Reactants
PE of the Activated Complex
PE of Products
Heat of Reaction
(∆H)
Ene
rgy
Reaction coordinate
Reactants
Products
Activation Energy
Activated Complex or Transition State
PE of the Reactants
PE of the Activated Complex
PE of Products
Heat of Reaction
(∆H)
PE of the Reverse Reaction