Dissolving
* No new substances are formed. The solid simply breaks down into its individual ions or molecules, which are then surrounded by water molecules.
* The process is usually reversible. You can often recover the original solid by evaporating the water.
* No gas is produced.
* No change in temperature (or a very small, insignificant change).
Reacting
* New substances are formed. The original solid chemically combines with water molecules, creating new compounds.
* The process is usually not easily reversible. You won't be able to get the original solid back by simply evaporating the water.
* Gas may be produced.
* There is a noticeable change in temperature. The solution may get hotter (exothermic reaction) or colder (endothermic reaction).
Examples:
* Dissolving: Salt (NaCl) dissolving in water. The salt breaks down into Na+ and Cl- ions, but the chemical composition of the salt itself hasn't changed. You can get the salt back by evaporating the water.
* Reacting: Sodium metal (Na) reacting with water. This produces sodium hydroxide (NaOH) and hydrogen gas (H2). The sodium has chemically reacted with water to form new substances. You can't simply get the sodium back by evaporating the water.
Practical Observations:
* Appearance: Does the solid disappear completely into the water, or do you see any visible changes in the solution (color change, cloudiness)?
* Heating/Cooling: Does the solution feel warmer or colder after the solid dissolves?
* Gas Production: Do you see bubbles forming?
* Smell: Does the solution have a new, distinct smell after the solid dissolves?
Important Note: Sometimes it can be tricky to tell the difference between dissolving and reacting. If you're unsure, it's always best to consult a reliable source of chemical information.
