Physical Vs. Chemical Change

Physical vs. Chemical Change

​​​​​​Chemical reactions allow chemists to predict and track changes in matter. They indicate how many products are formed, what those products are, and the phase of each product. 

Signs/Indications of a Chemical Reaction:

• Energy change (heat released or absorbed)
  • Exothermic reaction- heat energy released
  • Endothermic reaction- heat energy absorbed
• Production of gas
• Formation of precipitate
• Color change
• Change in odor or smell

Physical Changes:

• Changes in the appearance or form of a substance.
• Phase changes (solid, liquid, or gas)
• When something changes in a physical way, the chemical formula does not change because you end up with the same substance you started with.

Chemical changes produce new substances with new properties. New substances are formed during chemical changes, so
we can expect the products to have properties significantly different from the reactants. Heat, light, smoke, smells, bubbles, and changes in color often accompany chemical changes. The terms chemical change and chemical reaction mean the same thing.

DIssolving: 

Chemical equations can also represent the process of dissolving. 

eg: C₂H₆O (l) --> C₂H₆O (aq)

       HCl (g) --> HCl (aq)

Another way of writing the second equation: HCl (g) --> H⁺ (aq) + Cl⁻ (aq)

Ionic compounds do not dissolve the same way as molecular solids. This can be shows with an equation that stresses the formation of ions in solution. 

         Molecular substances do not break apart when dissolved so there is only one way to write the equation

Dissolving is generally considered a physical change, but it is common with chemical change as well