1. Collision Theory 2. Factors affecting rate 3. Investigate how concentration affects rate.
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1. Collision Theory 2. Factors affecting rate 3. Investigate how concentration affects rate
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Collisions & Activation Energy Next slide
Transcript of 1. Collision Theory 2. Factors affecting rate 3. Investigate how concentration affects rate.
1. Collision Theory
2. Factors affecting rate
3. Investigate how concentration affects rate
Collision Theory
1. For a reaction to occur the particles must collide
2. The colliding particles must have a minimum energy called the
Activation Energy
Collisions & Activation Energy
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Factors affecting Rate of reaction
1. Concentration
2. Particle size
3. Temperature
4. Presence of a catalyst
5. Nature of reactants
1. Effect of concentration on rateIncreasing concentration increases the rateBy increasing the number of collisions as there are more particles in same solution (space/volume)
The formation of a pale yellow precipitate of sulphur can be used to monitor the progress of
the reaction
HCl Na2S2O3 H2O+NaCl
Investigate the effect of concentration on reaction rate
+ + S+ SO2
To investigate the effect of concentration on reaction rate
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Add the HCl to the Na2S2O3 in the flask
Record the time taken for the X to disappearRepeat with different concentrations of Na2S2O3 Inverse the time to get the rate
Effect of concentration on rate
RATE
CONCENTRATION
Conclusion ?
Rate is directly proportional to concentration
1
Time
2. Effect of Particle size on rate
2. Effect of Particle size on rateSmaller particles increase rate of reaction
As smaller particles have a greater surface area, thus increasing the rate of collision/ sec
Fine particles can cause dust explosions e.g. coal mines
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The rate of release of CO2 gas can be used to monitor the progress of the reaction
HCl CaCO3 H2O +
Investigate the effect of particle size on reaction rate
+ + CO2CaCl2
Add the HCl to a large chips of CaCO3 in the flask
As CO2 is released the mass of the flask drops
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Record the time taken for the release of CO2 to end ( No further mass loss)
Repeat using the same mass of powdered CaCO3
and the same volume of HCl
And the same concentration of HCL
Result
Finely divided particles react faster than large particles
3. Effect of temperature on rateIncreasing temperature increases the rate
By increasing the number of collisions / secMore of the colliding particles have the min activation energy
The formation of a pale yellow precipitate of sulphur can be used to monitor the progress of
the reaction
HCl Na2S2O3 H2O+NaCl
Investigate the effect of temperature on reaction rate
+ + S+ SO2
To investigate the effect of temperature on reaction rate
Next slide
Add the HCl to the Na2S2O3 in the flask
Record the time taken for the X to disappearRecord the temperature after mixing
Inverse the time to get the rate
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Repeat at different temperatures
Effect of temperature on rate
RATE
TEMPERATURE
Conclusion ?
Rate increases with increasing temperature
1
Time
Effect of temperature on rate
RATE
TEMPERATURE
What is the main factor
increasing rate between A and B
Rate increases due to increased collisions /sec
1
Time
AB
Effect of temperature on rate
RATE
TEMPERATURE
What other factor caused the large
rate increase between B and C
More colliding particles have E Act
1
Time
C
B
Catalyst
A catalyst is a species that speeds up a chemical reaction without being chemically changed upon completion of the reaction. In other words, the mass of a catalyst is the same before and after a reaction occurs.
Only collisions involving particles with sufficient energy are sucessfull. Particles possessing less than the mininum energy simply bounce apart upon collision.
The number of successful collisions per unit of time be increased by lowering the threshold energy (or the activation energy)A catalyst provides an alternative pathway for the reaction - a pathway that has a lower activation energy.
The catalyzed pathway (shown as a dotted green line above) has lower activation energy
4. Nature of reactants affect the rate
4. Nature of reactants affects rate
Ionic reactions are fast
Na+Cl- Ag+NO3-+ = Ag+Cl-
+ Na+NO3-
Mix solutions of sodium chloride and silver nitrate
A precipitate of silver chloride forms instantly
Ions are free to move in solution....no bonds to break
Sodium chloride + Silver Nitrate
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The pale yellow precipitate of sulphur forms slowly as covalent bonds in the sodium thiosulfate must first
be broken before the reaction can occur
HCl Na2S2O3 H2O+NaCl+ + S+ SO2
Covalent reactions are slower than ionic
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