Experiment 1

Great Chemistry!

How is energy released in chemical reactions?

Objective: The objective of this experiment is to investigate in what ways energy is released in chemical reactions.

Review of Scientific Principles:

Picture energy as the movement of molecules. Energy is the rearrangement of chemical and nuclear bonds to achieve a more stable state. It is not a substance that can be held, seen, or felt as a separate entity. We cannot create new energy that is not already present in the universe. We can only take different types of materials in which energy is stored, change their state, and harness the energy that escapes from the system in order to use it to do work for us. If the released energy is not used, it will escape and be "wasted" as a change in motion, vibration, or light.

Different energy forms exist because people need a way to relate and measure different states of molecular motion. Chemical energy is the energy stored in the chemical bonds of molecules. Energy in the form of heat can be used to break chemical bonds. When the bonds are broken, their chemical energy is converted into more thermal, or heat, energy. When the heat energy is used to do work for us, we call it mechanical energy. Mechanical energy can either be potential which is stored energy, or kinetic which is the energy of motion. The sum of the potential and kinetic energy of an object is the amount of its total mechanical energy. If we transfer the energy through wires, it is called electrical energy which we use to power televisions and compact disc players. Two other types of energy are radiant, from the sun, and nuclear, from changes in the nuclear structure of atoms. While it is necessary to discuss these different types of energy, it is important to remember that energy is really the motion of molecules, electrons, or photons, and released by rearrangement of chemical or nuclear bonds.

Some additional vocabulary is needed to be able to record the results of this experiment accurately. Temperature is defined as the average kinetic energy, which is proportional to the average velocity, of all the molecules in a certain vicinity. Heat is the movement of molecules. A reaction is said to be exothermic if it produces heat (feels warm); endothermic if it uses more heat than it gives off (feels cool). Bond breaking is an endothermic process. Bond making is an exothermic change.

Applications: Eating meals, driving your car, and running a race are all examples of chemical reactions that release energy.

Materials and Supplies:

General Safety Guidelines:


Part 1

  1. Put on your safety goggles.
  2. Add Plaster of Paris to a paper cup until it is about half full.
  3. Add room temperature water to a beaker until it is about half full.
  4. Feel the outside of the cup and the beaker.
  5. Add the water to the Plaster of Paris and stir.
  6. Be sure to take note of the temperature changes of the outside of the cup as the Plaster of Paris hardens.
  7. Describe your observations in the data section for Part 1.

Part 2

  1. Avoid putting your face directly over the cup of ammonia -