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

End