Video Transcript
In which of these reaction profile
diagrams is the energy required to break chemical bonds the greatest?
Reaction profile diagrams are
graphs that represent the changes in the energies of substances during a
reaction. The 𝑥-axis represents the progress
of the reaction over time. And the 𝑦-axis represents the
energies of the substances during the reaction. The graph contains three main
parts. The first flat segment on the left
represents the reactants. The peak of the graph represents
the transition state. And the flat section on the right
represents the products. In order for a chemical reaction to
occur, enough energy must be absorbed to bring the reactants to the transition
state. This energy is called activation
energy. It’s the amount of energy needed to
break bonds and begin to rearrange atoms so product molecules can form.
We can determine activation energy
from the graph by finding the difference between the energy of the transition state
and the energy of the reactants. During the transition state,
reactant molecules have just the right amount of energy and the correct orientation
in space for product molecules to begin to form. As new bonds form in the product
molecules, energy is released. Finally, the difference between the
reactants and products’ energy is the enthalpy of the reaction, or Δ𝐻. However, we are not going to focus
on enthalpy in this video.
In this question, we are asked to
identify the reaction profile diagram in which the energy required to break chemical
bonds is the greatest. The energy needed to break the
chemical bonds is the activation energy. Let’s find the activation energy on
each of the reaction profile diagrams in the answer choices. The bottom-left segment of each
reaction profile represents the energy of the reactants. And the peak or maximum point of
each reaction profile represents the transition state. The vertical distance between these
two points on the graph is the activation energy.
In choice (A), the difference
between the transition state and reactants’ energy is the greatest, which means that
the energy required to break chemical bonds is also the greatest. The correct answer is choice
(A).
