Which of these reactions between
calcium metal and nitric acid will have the fastest rate of reaction? (A) Experiment one, (B) experiment
two, (C) experiment three, (D) experiment four, (E) experiment five.
The question describes a reaction
between calcium metal and nitric acid. A reaction between these species
will occur when reactant particles collide with sufficient energy and the correct
orientation. How quickly the reaction takes
place can be expressed by the rate of reaction.
Rate of reaction measures how
reactant or product concentration, mass, or volume changes over time. As reactions occur when particles
successfully collide, if the number of collisions increases, then the chance of a
successful collision will increase and the rate of reaction will increase. There are a number of factors that
can affect the number of collisions between reactant particles. So let’s take a look at the
conditions used in this experiment.
We can see that all of the
experiments use the same volume of nitric acid solution. But the concentrations of the
nitric acid solutions are different. We also see that the experiments
are run at different temperatures. No mention is made of the amount of
calcium metal used. So we’ll assume that it’s the same
for each experiment. To answer the question, we need to
know how concentration and temperature affect the number of collisions between
particles and therefore the rate of reaction.
Let’s start by considering
concentration. Concentration is the amount of
substance in a particular volume. When the concentration is low,
there will be fewer particles available to collide and the number of collisions will
be relatively low. As the concentration increases, the
number of particles available to collide will increase and the number of collisions
will increase. So increasing the concentration
will increase the rate of reaction. This means that experiments two,
four, and five will have a faster rate of reaction than experiments one and
three. As we want to know which experiment
has the fastest rate of reaction, we can eliminate answer choices (A) and (C).
Now let’s consider the effect
temperature has on the rate of reaction. At low temperatures, the particles
move slower and collide with less energy. As the temperature increases, the
particles gain energy and move faster. As the particles are moving faster
and with more energy, the particles will collide more often and are more likely to
collide with sufficient energy for a reaction to occur. So increasing the temperature will
increase the rate of reaction. Since experiment two is performed
at a higher temperature than experiments four and five, it should have the fastest
rate of reaction.
Therefore, the reaction between
calcium metal and nitric acid that will have the fastest rate of reaction is
experiment two, answer choice (B).