Which method would provide evidence to support the inference that this is an exothermic reaction?
add A and C
add E and D
subtract A from C
subtract E from D
The graph shown the potential energy diagram of the reaction "reaction pathway".
X-axis represents the reaction progress, the transformation from the reactants to the products passing via the transition state.
Y-axis represents the potential energy of the reactants and the products and also the intermediate.
As clear from the attached image "F" represents the position of the reactants of the reaction, "B" represents the position of the intermediate/transition state and "G" represents the position of the products of the reaction.
Region "A" is the potential energy difference between the intermediate "B" and the reactants "F" which represents the activation energy of the reaction "Ea". Activation energy "Ea" can be defined as the minimum energy that the reactants should posses to initiate the reaction.
Region "C" is the potential energy difference between the reactants "F" and the products "G" which represents the enthalpy change of the reaction "ΔH".
ΔH = pot. energy of the products "G" - pot. energy of the reactants "F".
If "ΔH" is positive this means that the reaction is endothermic and this occurs when the potential energy of the products is greater than that of the reactants.
If "ΔH" is negative this means that the reaction is exothermic and this occurs when the potential energy of the products is smaller than that of the reactants.
In our example, It is obvious that the energy of the reactants is greater than the potential energy of the products.
So, ΔH will have a negative value which means that the reaction is exothermic reaction.
Thus, the right choice is: "subtract E from D" would provide evidence to support the inference that this is an exothermic reaction.
