Question

Draw an energy diagram for each of the reactions described below. Properly label each diagram, including reactants, products, transition state, axis labels, scale (set the reactants at 0 kJ/mol), Delta H, and E_a. Exothermic by 43 kJ/mol; E_a = 95 kJ/mol Endothermic by 15 kJ/mol; E_a = 55 kJ/mol Which of the reactions will occur the fastest? Slowest? Assume equal temperatures, concentrations, and the same rate law for both reactions.) For which of the reactions would the reverse reaction be fastest? Slowest? (Make same assumptions.)

Answer 1

the vertical axis is labeled Energy (KJ/MOL) and the horizontal axis is labeled Time or Reaction Progress (seconds or minutes)

in the graph....

draw a straight short horizontal line. write the reactant component of the reaction on it. eg. HCl + NaOH

from the end of the line draw a curve (a maximum curve) and at the end of the curve draw another straight horizontal line and on it write the product component of the reaction eg. H2O + NaCl.

Since this was an exothermic reaction, the reactant line is higher than the product line. For an endothermic reaction, the reactant line is below the product line.

Exothermic reaction - Negative enthalpy change.
Endothermic reaction - Positive enthalpy change.

the enthalpy change is measured from the reactant line TO the product line, and read off the vertical axis.

Activation energy is the vertical length from the reactant line to the maximum of the curve.