A student is investigating the rate
of reaction for a certain reaction. They repeat an experiment four
times, changing the conditions each time. These are shown in the diagram
below. Which experiment would you predict
to have the greatest rate of reaction?
Rate of reaction measures how
reactant or product concentration, mass, or volume changes over time. We can think of the rate of
reaction as the speed of a chemical reaction. In this question, we want to know
which of the experiments has the greatest rate of reaction. In other words, in which experiment
does the reaction happen the fastest. We can see that all of the
experiments are performed at a different temperature and two of the experiments use
a catalyst. So we need to know how temperature
and the addition of a catalyst affect the rate of reaction. In order for a chemical reaction to
occur, particles must collide with enough energy and the correct orientation.
A catalyst is a substance that can
decrease the minimum amount of energy needed for a reaction to occur without
undergoing a permanent chemical change during the reaction. As less energy is needed for the
reaction to occur when a catalyst is added, the experiments where a catalyst is used
should be faster or have a greater rate of reaction than the experiments that do not
use a catalyst. So, we can eliminate answer choices
(B) and (D).
Now, let’s consider the effect
temperature will have on the rate of reaction. As the temperature increases, the
particles involved in a chemical reaction gain energy and move faster. The faster the particles move, the
more likely they are to collide with each other with enough energy for a reaction to
occur. So the rate of reaction tends to
increase with increasing temperature. Therefore, between the two
experiments that use a catalyst, the experiment at 40 degrees Celsius will have a
greater rate of reaction than the experiment at 20 degrees Celsius.
In conclusion, the experiment that
we predict to have the greatest rate of reaction is experiment (C), as this
experiment involves the use of a catalyst and is performed at the highest