Rates of Reaction
Increasing the Surface Area of a Solid.
A solid in a solution
can only react when particles collide
with the surface of the solid.
The bigger the area of the solid surface,
the more particles can collide with it per second,
and the faster the reaction rate is.
You can increase the surface
area of a solid by breaking it up
into smaller pieces (see also nanoparticles). A powder
has the largest surface area and has the fastest reaction rate.
This is why catalysts are often used as powders.
In the reaction between
calcium carbonate and dilute hydrochloric acid
HCl + calcium carbonate
calcium chloride + carbon
dioxide + water.
HCl(aq) + CaCO3(s) CaCl2(aq) + CO2(g) + H2O(l)
Calcium carbonate may be used in the form of marble chips.
The reaction rates of the same mass of large marble
and small marble chips can be compared - see below.
The reaction can be followed
by plotting the loss of mass against time.
The reaction rate is
faster (the slope is steeper) for
the reaction with small marble chips (greater surface area).
Note that the final loss of mass is
the same for
both reactions. This is because the same mass
of calcium carbonate (marble chips) will produce the
same mass of carbon dioxide whether the chips are
large or small. The smaller chips will just do it more quickly.
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