Question

The potential energy diagram for a reaction $X \to$Y is given. A and C in the graph corresponds to:
A.A$\to$Activation energy, $C \to \Delta {H^ \circ }$
B.A$\to$Energy of reactants, $C \to$energy of products
C.$A \to \Delta {H^ \circ },C \to$Activation energy
D.$A\xrightarrow{{}}$Activation energy, $C \to$Threshold energy

Answer 1

We can say the changes in energy which takes place during a chemical reaction could be shown in a diagram known as a potential energy diagram, or sometimes known as reaction progress curve. A potential energy diagram represents the change in potential energy of a system as reactants are changed into products.

Complete step by step answer:
We have to know that the Arrhenius equation is helpful in calculating the rate of reaction and plays an important portion in chemical kinetics. We can write Arrhenius equation as,
$K = A{e^{ - {E_a}/RT}}$
Here, K is the rate constant
A is the pre-exponential factor
${E_a}$ is the activation energy
R is the gas constant
T is the temperature (in Kelvin)
With an increase in temperature, the rate of the reaction also increases. This means that temperature and rate are proportional. Kinetic energy also increases with respect to temperature. Therefore, when we raise the temperature, the number of molecules with kinetic energy is greater than the increase in activation energy. This leads to increase in the rate of the overall reaction with reduction in the activation energy.
The activation energy ${E_a}$of a reaction is the boundary which must be overcome for the reactants to be converted to become products. When the activation energy is low, the reaction is likely to be fast. The activation energy is high, the reaction is likely to be slow.
We can define activation energy as the least possible amount of energy (minimum) that is required to begin a reaction or the amount of energy available in a chemical system for a reaction to take place $\to A$.
The difference in the energies of the forward and backward reactions is given by ${\Delta H^{o}. C \to \Delta H^ \circ }$.
Therefore, the correct option is (A).

Note:
For a chemical reaction an energy profile (or reaction coordinate diagram) is a theoretical representation of a single energetic pathway, along the reaction coordinate, as the reactants are converted into products. Reaction coordinate diagrams are obtained from the corresponding potential energy surface (PES) that are used in computational chemistry to model chemical reactions by correlating the energy of a molecule(s) to its structure (within the Born–Oppenheimer approximation). The reaction coordinate is a parametric curve which follows the pathway of a reaction and shows the progress of a reaction.