For example, a solution between potassium nitrate and water is more endothermic than sodium nitrate in water. Can someone explain?
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1$\begingroup$ We could compare the relative stabilities (which can be deduced from their enthalpy changes of formation) of the products and reactants. If the products are less stable, compared to reactants, the reaction is endothermic. Also, more quantitatively, we could also calculate the energies absorbed and released from the specific processes that occur. For example, in dissolution, we would have to look at the enthalpy changes of hydration of the ions and the lattice energies of the ionic compounds. $\endgroup$– Tan Yong BoonJun 30, 2018 at 7:00
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$\begingroup$ But what specifically makes a reaction like the solution between potassium nitrate and water have a greater enthalpy change than the solution of sodium nitrate in water. $\endgroup$– Sony BingJun 30, 2018 at 7:04
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$\begingroup$ Notice that the positive ion has changed from Na+ to K+. This would significantly change the enthalpy change of hydration of the ions, since it would then be less exothermic as a result of potassium ion's ionic radius being considerably larger than that of the sodium ion's. This may have tipped the balance between the lattice energy and the enthalpy change of hydration, resulting in the overall process becoming endothermic. $\endgroup$– Tan Yong BoonJun 30, 2018 at 7:23
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$\begingroup$ By the way, if you only concerned with the process of solution. You might want to make it clear in the question title. It seems too general currently. $\endgroup$– Tan Yong BoonJun 30, 2018 at 7:24
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$\begingroup$ So the larger the atomic radius, the weaker the bond energies which makes the reaction less exothermic/more endothermic? $\endgroup$– Sony BingJun 30, 2018 at 12:20
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