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not referring to size of particles such as atoms, ions, molecules. particle size refers to the physical dimensions of a reactant in solid state.
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By breaking large particle into smaller pieces →the surface area increases even though total mass and total volume remains the same.
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increased surface area → allows for more effective collisions to occur.
More total exposed surface area in contact with other reactants.
Sample
Rate of Reaction increases with decrease in particle size
- there is larger total exposed surface area of the reacting particles to collide into.
- thus resulting in more collisions between reacting particles per unit time
- thus frequency of effective collisions increases
- hence rate of reaction increases
Sample
Rate of Reaction decreases with increase in particle size
- there is smaller total exposed surface area of the reacting particles to collide into
- thus resulting in less collisions between the reacting particles per unit time
- thus frequency of effective collisions decreases
- hence rate of reaction decreases
→ please do not write surface area to volume ratio.
Real Example Explain why marble chips instead of powdered marble slows down ROR between hydrochloric acid and calcium carbonate in the marble
- marble chips have larger particle size compared to powdered marble thus marble chips have smaller total exposed surface area for the reacting particles (of HCl or H+) ions to collide into
- this results in fewer collisions between reacting particles (of calcium carbonate and hydrochloric acid or reacting particles of calcium carbonate and H+ ions) per unit time
- thus frequency of effective collision decreases and the rate of reaction decreases
Note
A data logger can be used when the reaction is too vigorous for data to be collected manually. Chemistry Practical Notes
Summary
Increase in the surface area of solid reactants (i.e. a reduction in particle size) results in an increase in the rate of reaction
Note
Particle size of catalyst used could be compared instead of particle size of reactant Catalysts and their Affect on ROR
note: just write powdered form in exam to avoid confusion.