Final answer:
To calculate the standard enthalpy change for the given reaction, you need to use the standard enthalpies of formation for the reactants and products. You can use the formula AH° = (sum of products' enthalpies) - (sum of reactants' enthalpies) to calculate the change in enthalpy.
Step-by-step explanation:
The standard enthalpy change for the reaction 4a + 2b → 2ab + a2 can be calculated by using the standard enthalpies of formation for the reactants and products.
First, we need to identify the reactants and products. In this case, the reactants are a and b, and the products are ab and a2.
We can use the formula AH° = (sum of products' enthalpies) - (sum of reactants' enthalpies) to calculate the standard enthalpy change. For example, AH° = (2 * enthalpy of ab + enthalpy of a2) - (4 * enthalpy of a + 2 * enthalpy of b).