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Chemistry A level Question

Suggest why the addition of anhydrous magnesium chloride to water resultsin an increase in temperature?

The markscheme says that the answer is" the bonds created between the Mg2+ and cl- ion release energy as bond making is exothermic"

I dont understand as I thought when ionic compounds dissolve they are pulled apart due to the electrostatic attractions between the polar water molecules and the ions. Why are they bonding together again?

Thanks:smile:
Reply 1
any ideas?
Reply 2
When Magnesium Chloride dissolves in water, the Mg2+ and Cl- ions dissociate in solution, of course energy is required to break the lattice structure. However, an excess of energy is in fact released from the ionic bond making of water molecules surrounding the Mg2+ and Cl- ions, so-called 'clustering' of water molecules. Overall, more energy is released from the process of dissolving/bond making, this means the reaction is exothermic. Hence an increase in temperature.

This image shows a similar situation when Sodium chloride dissolves, notice the partial negative and partial positive charges of a water molecule.

dissolving.jpg
Reply 3
Original post by RDB1826
When Magnesium Chloride dissolves in water, the Mg2+ and Cl- ions dissociate in solution, of course energy is required to break the lattice structure. However, an excess of energy is in fact released from the ionic bond making of water molecules surrounding the Mg2+ and Cl- ions, so-called 'clustering' of water molecules. Overall, more energy is released from the process of dissolving/bond making, this means the reaction is exothermic. Hence an increase in temperature.

This image shows a similar situation when Sodium chloride dissolves, notice the partial negative and partial positive charges of a water molecule.

dissolving.jpg


Thank you!

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