Chemistry lessons can be learned using common household materials that are not dangerous to keep on hand. Vinegar, baking soda, steel wool, a plastic cup and a thermometer are all that is needed to demonstrate exothermic and endothermic reactions. Wear protective glasses to keep from splashing the liquids in your eyes during the experiments, and try not to inhale the fumes from vinegar which can irritate your nose.
Endothermic reactions are identified by a drop in temperature. Endothermic reactions need to take heat out of the surroundings to get the energy necessary to form the products. As a result, the measured temperature of the system decreases. In chemistry, a change is energy is described as a change in enthalpy. Endothermic reactions have a positive change in enthalpy because the energy inside the reaction system increases as energy is taken from the surroundings. An endothermic reaction can be demonstrated using vinegar and baking soda.
Vinegar and Baking Soda
Vinegar is acetic acid, and baking soda is sodium bicarbonate. The reaction between acetic acid and sodium bicarbonate makes solid sodium acetate, liquid water and carbon dioxide gas. Pour 2 teaspoons of vinegar into a plastic cup. Place the end of the thermometer in the vinegar until a stable temperature can be recorded. Leave the thermometer in the cup, and add 1/2 teaspoon of baking soda to the vinegar. Watch the thermometer and record the drop in temperature.
Exothermic reactions are identified by an increase in temperature. Exothermic reactions need less energy to break the bonds of the reactants than is released when forming the products. Therefore, the difference between the energy going into the reaction and the energy leaving the reaction results in energy flowing into the surroundings as heat. This means exothermic reactions have a negative change in enthalpy because the energy inside the reaction system decreases. Vinegar and steel wool can be used to demonstrate an exothermic reaction.
Vinegar and Steel Wool
Vinegar dissolves the protective coating on steel wool that keeps the steel from oxidizing and rusting with oxygen in the air. Oxidation is an exothermic reaction. Place the steel wool and a thermometer in a covered, dry plastic cup to get a stable temperature measurement. Remove the thermometer and soak the steel wool in vinegar for approximately one minute to dissolve the protective coating. Remove the steel wool from the vinegar and squeeze out all the excess liquid. Wrap the steel wool around the thermometer and place both back into a covered, dry cup. Record the increase in temperature over several minutes.