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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?

Saturday
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  • 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. – Andrea Pellegrini Feb 13 '22 at 07:49
  • @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. – Poutnik Feb 13 '22 at 08:17
  • 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. – Poutnik Feb 13 '22 at 08:24
  • @Poutnik Thanks for commenting. So, does the heat capacity increase or decrease? + How much will it change? – Saturday Feb 13 '22 at 08:35
  • 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. – Poutnik Feb 13 '22 at 08:50
  • Very closely related: does-enthalpy-of-dissolution-change-with-temperature // Also related Wikipedia: Enthalpy_change_of_solution – Poutnik Feb 13 '22 at 09:18
  • To expand on what Poutnik said, if you dissolve, say, salt in water, the physical states of the salt and water both change. The salt changes from solid to aqueous, and the water changes from only interacting with itself to interacting with both itself and the Na+ and Cl– ions. So, by definition, the heat capacity of the solution will be different from the sum of the heat capacities of the individual components. The ques., though, is how much different (and whether it's more or less) and whether that diff. is significant for your calcs. The only way to know that is to look up the actual data. – theorist Feb 14 '22 at 04:58

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