Video Transcript
The reaction between warm
hydrochloric acid and magnesium has a faster rate of reaction than the reaction
between cold hydrochloric acid and magnesium. Which statement explains this
observation? (A) The particles are more
concentrated and have a greater mass. (B) The particles are moving faster
and have a greater surface area. (C) The particles are moving faster
and have a greater mass. (D) The particles are more
concentrated and have greater energy. Or (E) the particles are moving
faster and with greater energy.
The rate of a chemical reaction is
the rate at which reactants are converted into products. We can think of this as the speed
of a chemical reaction. We are told in the question that
two reactions between hydrochloric acid and magnesium are carried out. We are also told that the reaction
using warm hydrochloric acid has a faster rate of reaction than the reaction using
cold hydrochloric acid. We need to determine which
statement explains this observation.
We can use collision theory to help
us. Collision theory states that
reactions only happen when particles collide with sufficient energy and the correct
orientation. According to this theory, if the
collision frequency or the energy of the collisions increase, then the rate of
reaction will increase. As the difference between the two
reactions is the temperature of the hydrochloric acid, we should consider how
temperature might affect the collision frequency or energy of the collisions.
We may recall that the speed of a
particle depends on temperature. At cold temperatures, particles
move about relatively slowly. As the temperature increases, the
particles gain kinetic energy and move faster. This means that at higher
temperatures, the particles collide more often and with more energy. Thus, increasing the temperature
will increase the rate of reaction.
So we now know that the reaction
between warm hydrochloric acid and magnesium has a faster rate of reaction than the
reaction between cold hydrochloric acid and magnesium because the particles are
moving faster and with greater energy, answer choice (E).
