I need the molar enthelpy of formation

[cscott]

I have a chemical equation and the molar enthalpies of formation for its products, along with the total change in enthalpy for the reaction. With this I can easily find the total enthalpy of the reactants. In this case, there are two reactants and I need the molar enthalpy of formation of one of them. How can I achieve this knowing nothing about the second reactant?

 

[maverick280857]

I have a chemical equation and the molar enthalpies of formation for its products, along with the total change in enthalpy for the reaction. With this I can easily find the total enthalpy of the reactants. In this case, there are two reactants and I need the molar enthalpy of formation of one of them. How can I achieve this knowing nothing about the second reactant?

Only if you are computing the standard molar enthalpy of formation...if one of the reactants is in its most stable allotropic form, its enthalpy of formation is zero (because it exists that way in the standard state anyway so you don't have to form it...look up the textbook for a list of allotropes which are assigned a standard molar enthalpy of formation equal to zero).

 

[Blueshift5]

To determine the molar enthalpy of formation for the first reactant, you will need to use the equation:

ΔH°rxn = ΣnΔHf°(products) - ΣmΔHf°(reactants)

Where ΔH°rxn is the total change in enthalpy for the reaction, ΣnΔHf°(products) is the sum of the molar enthalpies of formation for the products, and ΣmΔHf°(reactants) is the sum of the molar enthalpies of formation for the reactants.

Since you have the chemical equation and the molar enthalpies of formation for the products, you can easily calculate the sum of the molar enthalpies of formation for the products. However, as you mentioned, you do not have the molar enthalpy of formation for one of the reactants. In this case, you will need to use the molar enthalpy of formation for the second reactant as a variable in the equation.

You can do this by assigning a variable, such as x, to represent the molar enthalpy of formation for the second reactant. This will allow you to solve for x using algebraic methods. Once you have solved for x, you can substitute the value into the equation to find the molar enthalpy of formation for the first reactant.

It is important to note that the accuracy of this method will depend on the reliability of the molar enthalpies of formation for the products and the total change in enthalpy for the reaction. It is always recommended to use multiple sources and to double check your calculations to ensure the most accurate results.