Before we observe a synthesis reaction, let's review the transfer of energy that occurred in lesson 3 when an ionic compound split apart in water.

In that simulation we saw that a water molecule slowed down and seemed to lose kinetic energy when it collided with the ionic compound KI. This collision caused the ionic compound KI to split into a K⁺ cation and an I⁻ anion.

If we put together two concepts from the homework and lesson 3, we can come to a conclusion about where the kinetic energy from the water went. 

• Potential energy can be converted to kinetic energy, and kinetic energy can be converted back to potential energy.
• Energy can be transferred from the system to the surroundings, or from the surroundings into the system.

Recall that the water temperature at the beginning of our simulation experiment contained a certain amount of kinetic energy. That kinetic energy decreased the moment the water collided with the ionic compound and it subsequently broke apart. That kinetic energy must have transferred into the system.