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 Next slide

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 rate Increasing concentration increases the rate By 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 HClNa 2 S 2 O 3 H2OH2O + NaCl Investigate the effect of concentration on reaction rate ++ S + SO 2

To investigate the effect of concentration on reaction rate Next slide Add the HCl to the Na 2 S 2 O 3 in the flask Record the time taken for the X to disappear Repeat with different concentrations of Na 2 S 2 O 3 Inverse the time to get the rate

Effect of concentration on rate RATERATE CONCENTRATION Conclusion ? Rate is directly proportional to concentration 1 Time

2. Effect of Particle size on rate

Smaller 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 Next slide

The rate of release of CO 2 gas can be used to monitor the progress of the reaction HClCaCO 3 H2OH2O+ Investigate the effect of particle size on reaction rate ++ CO 2 CaCl 2

Add the HCl to a large chips of CaCO 3 in the flask As CO2 is released the mass of the flask drops Next slide

Record the time taken for the release of CO 2 to end ( No further mass loss) Repeat using the same mass of powdered CaCO 3 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 rate Increasing temperature increases the rate By increasing the number of collisions / sec More 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 HClNa 2 S 2 O 3 H2OH2O + NaCl Investigate the effect of temperature on reaction rate ++ S + SO 2

To investigate the effect of temperature on reaction rate Next slide Add the HCl to the Na 2 S 2 O 3 in the flask Record the time taken for the X to disappear Record the temperature after mixing Inverse the time to get the rate

Next slide Repeat at different temperatures

Effect of temperature on rate RATERATE TEMPERATURE Conclusion ? Rate increases with increasing temperature 1 Time

Effect of temperature on rate RATERATE TEMPERATURE What is the main factor increasing rate between A and B Rate increases due to increased collisions /sec 1 Time A B

Effect of temperature on rate RATERATE 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 + NO = Ag + Cl - + Na + NO 3 - 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 next

The pale yellow precipitate of sulphur forms slowly as covalent bonds in the sodium thiosulfate must first be broken before the reaction can occur HClNa 2 S 2 O 3 H2OH2O + NaCl ++ S + SO 2 Covalent reactions are slower than ionic

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