Question

How does an increase in surface area affect the rate of a chemical reaction?

Answer 1

Smaller sized blocks of reactant have a greater surface area to volume ratio than larger blocks. This means that they have more particles on the surface so there are more collisions per second. And increase in surface area.

Complete step by step answer:
To understand this we should consider first the collision theory.
Which states that chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy.
The role of a chemical reaction is determined by the frequency of successful collisions.
Frequency means: Number of successful collisions per second.
When particles in the solution react they can only react with particles on the surface of that molecule or compound.
The particles that are not on the surface do not have contact with solution and hence they don’t react.
But when that molecule is divided into further particles the surface area increases, that is there are more particles on the surface to react.
Now the surface area has increased. Because we have more collisions per second, the rate increases when we increase the surface area.
When you grind a solid into fine powder now the same number of moles of reactant exist in a greater surface area from.
Final Answer:
Thus we can conclude here, that in the absence of any other change, increasing surface area to volume ratio increases the rate of reaction.

Note:
Surface area is only one factor that affects rate but if you increase the surface area, and also drop the temperature, you may find that there is no overall change in rate, because the effect of the change is nullified by the other.