2. • Chemical reaction is a process in which a substance of substances is/are changed into one or more
new substances. In a chemical reaction, one or more reactants change into one or more products.
They are represented by chemical equations. Chemical equations are symbolic representations of
chemical processes. They use chemical symbols to show what happens during a chemical reaction
• Consider what happens when hydrogen gas (H2) burns in air (which contains oxygen, O2) to form
water (H2O)
• This reaction can be represented by the chemical equation
• The “plus” sign means “reacts with” and the arrow means “to yield.”.
• Therefore, if we read the equation, it will be: Molecular hydrogen reacts with molecular oxygen
to yield water.
3. • Reactants are the starting materials in a chemical reaction. In the chemical
equation above, hydrogen and oxygen are the reactants. Reactants are found
on the left side of the chemical equation.
• Product is the substance formed as a result of a chemical reaction. In the
chemical reaction above, water is the product. Products are found on the
right side of the chemical equation.
4. The following are the signs and evidences that a chemical reaction has occurred:
1.Production of Light
Ex: Burning a magnesium ribbon
2. Production of Gas or Bubbles
Ex: Baking Soda in Vinegar
3. Change in the temperature of the substance
Ex: Baking soda added in water makes the water’s temperature rise
slightly
4. Change in color
Ex: Tarnishing silver or burning a wood
5. Formation of a precipitate. Precipitates are insoluble solids formed during a
chemical reaction.
6. Odor is observed
Ex: Rotting food
