Journal Entry:

Dissolving an ionic solid in water is a multistep process in which three distinct processes must occur. The three steps are:
1. The separation of ions in the solid
2. The separation of particles in the solvent (water)
3. The formation of ion-dipole interactions between the ions and the water molecules.

What is the ΔH of each step?
(A) All of the steps are either endothermic or exothermic, depending on the ΔH of solution of the solute/solvent pair.
(B) Steps 1 and 2 are endothermic and step 3 is exothermic.
(C) Steps 1 and 2 are exothermic and step 3 is endothermic.
(D) Steps 1 and 2 are either both endothermic or both exothermic depending on the solute and solvent, but step 3 is always the opposite.

Learning Intentions

●     We will learn about the energy transformations and particle changes involved in dissolving a variety of solutions.

●     We will learn how to follow and modify a procedure and interpret collected data in which calorimetry is used to create an ideal, cost effective hand warmer.

Closing Task:

You can create a procedure to determine an ideal cost effective hand warmer using ionic solids and water.

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)

Calorimetry is an experimental technique that is used to determine the heat exchange/transferred in a chemical system. (EK 5.B.4)

 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)