Rates of Reaction

Measuring the Rate of any Reaction.

The rate of a chemical reaction can vary greatly.
A reaction, may be very slow
, an example is rusting,
or very fast, an example is a firework exploding.

The rate of a reaction may be measured by following
the loss of a reactant, or the formation of a product.

Rate of reaction = amount of reactant used ÷ time.
Rate of reaction = amount of product formed ÷ time.

The following three reactions may
be studied to show how the rate can be changed.

They are

1) The reaction between
calcium carbonate and dilute hydrochloric acid - see below.

2) The reaction between
sodium thiosulfate solution and dilute hydrochloric acid.

3) The decomposition of hydrogen peroxide solution.

Measuring the Rate of the Reaction
between Calcium Carbonate and dilute Hydrochloric Acid.

HCl + calcium carbonate arrow calcium chloride + carbon dioxide + water.
HCl(aq)   +     CaCO3(s)    arrow         CaCl2(aq)      +     CO2(g)   +     H2O(l)

The rate of this reaction can be measured
by following the rate at which carbon dioxide is formed.

This can be done by having the reaction in an
open flask on an electric balance (weighing machine).
As the carbon dioxide escapes to the air,
the mass of the flask will decrease.
You can take a reading from the balance every 30 seconds,
then plot a graph of loss of mass against time.

The gradient of the plot (the steepness of the slope)
shows the rate of the reaction (how fast it is going).

See also increasing the surface area of a Reaction.

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