Calculating the enthalpy of reaction at non-standard concentration for reactions in aqueous phase

Standard conditions for a chemical reaction in the aqueous phase, for instance, a chemical reaction in solution, consider that reagents should be at a 1 M concentration. I was wondering how to calculate the $\Delta$H for other concentrations. Let's say we have the next reaction:


$$\ce{2HCl(aq) + Na2CO3(aq) -> 2NaCl(aq) + CO2(g) + H2O(l)}$$


It resumes to:


$$\ce{2H+(aq) + CO3^{2-}(aq) -> CO2(g) + H2O(l)}$$


To determine the $\Delta H^0$ we can perform:


$\Delta H^0$ = $\Delta H^0\_{f}$ $\ce{CO2(g)}$ + $\Delta H^0\_{f}$ $\ce{H2O(l)}$ - 2$\Delta H^0\_{f}$ $\ce{H+(aq)}$ - $\Delta H^0\_{f}$ $\ce{CO3^{2-}(aq)}$


Which results in: - 3 kJ/mol


But this is assuming standard conditions and thus 1 M concentrations for the reagents in the aqueous phase. How can I calculate the $\Delta H$ for other concentrations, for instance, when mixing 100 mL of 0.2 M $\ce{HCl(aq)}$ with 50 mL of $\ce{Na2CO3(aq)}$ 0.3 M?


