Hess'slaw can be applied to calculate the reaction is?
Enthalpy
the wording in your question makes no sense to me.
To calculate the reaction enthalpy using Hess's Law, follow these steps:
1. Write down the balanced chemical equation for the desired reaction.
2. Identify any other reactions whose enthalpies are known and can be combined to obtain the desired reaction.
3. Multiply the reaction equation(s) by appropriate coefficients to match the desired reaction equation.
4. If necessary, reverse the direction of the reaction equation(s) to match the desired reaction equation.
5. Add the enthalpies of the individual reactions together to obtain the enthalpy of the desired reaction.
Hess's Law states that the enthalpy change of a reaction is the same regardless of whether the reaction occurs in a single step or through a series of intermediate steps. This means that you can break down a reaction into its constituent steps, find the enthalpy changes for each step (using known enthalpies), and then add them up to get the overall enthalpy change.
For example, let's say you want to calculate the enthalpy change for the reaction:
2H2(g) + O2(g) → 2H2O(g)
You know the enthalpies of the following reactions:
1) H2(g) + 1/2O2(g) → H2O(g) ∆H = -286 kJ/mol
2) H2(g) + 1/2O2(g) → H2O(l) ∆H = -285.8 kJ/mol
To calculate the enthalpy change for the desired reaction, you can subtract the enthalpy of reaction 1 from reaction 2:
∆H = -285.8 kJ/mol - (-286 kJ/mol) = 0.2 kJ/mol
Therefore, the enthalpy change for the reaction 2H2(g) + O2(g) → 2H2O(g) is 0.2 kJ/mol.