Standard heats of formation for reactants and products in the reaction below are provided. 2 HA(aq) + MX2(aq) → MA2(aq) + 2 HX(l) Substance ΔHf° (kJ/mol) HA(aq) -357.05 HX(l) -449.579 MA2(aq) -63.958 MX2(aq) 69.602 What is the standard enthalpy of reaction, in kJ? Report your answer to three digits after the decimal.

Answer : The standard enthalpy of reaction is, -318.618 kJ

Explanation :

Enthalpy change : It is defined as the difference in enthalpies of all the product and the reactants each multiplied with their respective number of moles. It is represented as

The equation used to calculate enthalpy change is of a reaction is:  

The equilibrium reaction follows:

The equation for the enthalpy change of the above reaction is:

We are given:

Putting values in above equation, we get:

Thus, the standard enthalpy of reaction is, -318.618 kJ

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !