Journal Entry:

The enthalpy of a solution of NaCl crystals in H₂O is 3.87 kJ/mol NaCl at 298K. The conclusion is

(A) the dissolution of sodium chloride is nonspontatneous but occurs because the temperature is high.
(B) the separation of solid ions and water molecules requires more energy than the energy released from the attraction of water molecules to ions.
(C) every step in the dissolution process is endothermic, but only slightly.
(D) the attraction of water molecules to ions is greater than the sum of the repulsion between the sodium and chloride ions and between the water molecules for each other.

Learning Intentions

• We will learn the three processes that cause a system to change its energy.

• We will learn about the energy transformations and particle changes involved in dissolving and diluting solutions.

• We will learn how to write enthalpy of reaction equations for dissolving solids.

Closing Task:

You can write a enthalpy of reaction equation for dissolving solids

Content Standards being covered:

Chemical system undergo three main processes that change their energy: heating/cooling, phase transitions, and chemical reactions. (E.K. 5.B.3.)

At the particulate scale, chemical processes can be distinguished from physical processes because chemical bonds can be distinguished from intermolecular interactions. (E.K. 5.D.2)

 The net energy change during a reaction is the sum of the energy required to break bonds in the reactant molecules and the energy release in forming the bonds of the product molecules. The net change in energy may be positive for endothermic reactions where energy is required, or negative for exothermic reactions where energy is released. (E.K. 5.C.2)