Is the heat capacity of a solution the sum of the heat capacities of the solvent and the solute?

Based on what I have learned, specific heat is determined by the interaction between molecules. This explains water's large specific heat because it has many hydrogen bonds which take a large portion of the supplied heat to break and only the rest actually increases the temperature.

When the solute dissolves into the solvent, I assume the bonds between the molecules strengthen, so the total heat capacity increases. Is this correct?

If I am correct, is the change in heat capacity negligible or significant enough to take into calculation?

  • $\begingroup$ Yes, it is. Heat capacity it's defined by the solvent and the solute, in proportion to its concentration. Usually, you'll find the heat capacity of a NaOH 30% solution and of a NaOH 10% solution which Is slightly different. $\endgroup$ Commented Feb 13, 2022 at 7:49
  • $\begingroup$ @AndreaPellegrini But this is obvious, as different ratios of both with the same total mass, sitting side by side, would have different heat capacity either. The question is about heat capacity of mixed versus separated. $\endgroup$
    – Poutnik
    Commented Feb 13, 2022 at 8:17
  • $\begingroup$ You could keep specific heat. It is intensive property, while heat capacity is extensive. For the same total mass, their ratios for different systems are the same. // If you consider the nature of specific or molar heat capacities, it should be clear they must generally change by dissolution. $\endgroup$
    – Poutnik
    Commented Feb 13, 2022 at 8:24
  • $\begingroup$ @Poutnik Thanks for commenting. So, does the heat capacity increase or decrease? + How much will it change? $\endgroup$
    – Saturday
    Commented Feb 13, 2022 at 8:35
  • $\begingroup$ Yes, it does. This much. It is case specific and rather experimental value, hard to be predicted. Aside of the direct heat capacity measurement, it can be determined by temperature dependence of dissolution enthalpy. $\endgroup$
    – Poutnik
    Commented Feb 13, 2022 at 8:50


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