Question

Which of the following best helps to why the value of Delta H degree for the CaF_2 in water in positive? A. CaF_2(s) is insoluble positiveB. CaF_2(s) dissolves in water CaF_2 (aq) particles C. Ca^2+ ions have very strong interactions with F^- ions in the crystal lattice. D. Ca^2+ ions have very strong ion - dipole interactions with water molecules in the

Answer 1

Answer: Option (C) is the correct answer.

Explanation:

A positive value of enthalpy or $\Delta H$ means that energy is being absorbed from the surrounding. As $CaF_{2}$ has strong ionic bonding between both calcium and fluorine atoms. So, to break their bond we need to provide energy to it.

So, when $CaF_{2}$ is dissolved in warm water then warm water molecules will bombard with the stable bond of $CaF_{2}$. As a result, the energy will transfer from water to the bond in order to break it. And, due to loss in internal energy then there will be consequent lowering of temperature.

When this bond is broken down then the atoms will separates into gaseous ions and these ions will be then surrounded by the water molecules. As ithe bond between  $CaF_{2}$ is very strong hence, its lattice energy will be very high.

Thus, we can conclude that the statement $Ca^{2+}$ ions have very strong interactions with $F^{-}$ ions in the crystal lattice, best helps to why the value of $\Delta H$ degree for the $CaF_{2}$ in water in positive.