THE NATURE OF CHEMICAL REACTIONS BY MS. PACHECO

In a chemical reaction… substances are changed so as to have different physical and chemical properties.

Reactants are… the ingredients in a chemical reaction found on the left of the “yields” (  )sign

Products are… what is produced in a chemical reaction found on the right of the “yields” (  ) sign

Why do chemical reactions occur? For substances to gain a complete set of valence electrons, therefore becoming more stable

Also… Some reactions also require energy in order to occur!

Signs that a chemical reaction has occurred…. 1. A gas is evolved (produced). –Substance will bubble or fizz

Signs that a chemical reaction has occurred…. 2.A precipitate (ppt) forms. (A solid) –Substance will get cloudy, milky or a solid will actually be observed.

Signs that a chemical reaction has occurred…. 3.An energy change occurs. –A temperature change is noted by touching the container.

Have you noticed that… Real silverware will tarnish when in contact with eggs or egg products? What’s happening?

Ag + S  Ag 2 S Silver combines with the sulfur in eggs and other foods to produce silver sulfide.

Ag + S  Ag 2 S What are the reactants? What are the products? How is the equation read?

The reactants are silver and sulfur. Silver sulfide is the product

The equation is read as “silver and sulfur react to form silver sulfide”

Speaking of that tarnished silver… To clean it, put the silver in a dishpan so that it is underwater. Put in a piece of aluminum foil, so that it is touching the silver. Wait 30 minutes. See shiny “new” silver!!!

What happened? The aluminum “replaces” the silver in the silver sufide. Al + Ag 2 S  Ag + Al 2 S 3 Balanced equation 2Al + 3Ag 2 S  6Ag + Al 2 S 3

What are the reactants? What are the products? How is the equation read?