The potential energy diagram below refers to the reversible reaction involving reactants R and products P - Scottish Highers Chemistry - Question 1 - 2018

To find the enthalpy change for the reverse reaction, we need to determine the difference in potential energy between the reactants and products.

From the diagram, the potential energy of reactants R is approximately 40 kJ mol⁻¹ and that of products P is around 80 kJ mol⁻¹. The enthalpy change ( ( \Delta H ) ) can be calculated using the formula:

$\Delta H = E_{products} - E_{reactants}$

Substituting the values:

$\Delta H = 40 \, \text{kJ mol}^{-1} - 80 \, \text{kJ mol}^{-1} = -40 \, \text{kJ mol}^{-1}$

Since we are interested in the reverse reaction, we reverse the sign of our calculation:

Thus, the enthalpy change for the reverse reaction is +40 kJ mol⁻¹. Therefore, the correct answer based on the options given is B) +10 kJ mol⁻¹.