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Develop a Model to Show the Release or Absorption of Energy from a Chemical Reaction System

In this project, you will develop a model of a chemical reaction that either releases energy or absorbs energy. Whether a reaction releases or absorbs energy depends on the overall difference in the bond energies of the reactants and products. Your model should show the relationships between the parts of the system. These parts are the molecules and atoms that take part in the reaction. The model should also distinguish the reaction system from other systems.

Background

Atoms are the basic units of the types of matter known as elements. Very few elements exist in nature as single atoms. Most elements exist as atoms joined together into compounds by chemical bonds. During a chemical reaction, bonds are broken, atoms are rearranged, and new substances with new bonds form. Energy must be absorbed in order to break bonds, and energy is released when bonds form.

For any given compound, the amount of energy that will break its bonds and the amount released when the same bonds form are the same. For example, 1 mole of water molecules must absorb 1,840 kJ of energy for its bonds to break. And, when 1 mole of new water molecules form, the same amount of energy (1,840 kJ) is released. The amount of energy needed to break or form

1 mole of a certain type of bond is called bond energy.

As a reaction proceeds, the total bond energy of the reaction system changes. The total change in the bond energy depends on two factors:


1) the energy absorbed by the initial molecules (reactants) in order to break their bonds, and


2) the energy released as the bonds in the molecules that result (products) form.


For example, if breaking the reactants' bonds requires less energy than is released as the bonds of the products form, then the chemical reaction releases energy. This is what the graph on the left below shows. A chemical reaction that releases energy overall is called an exothermic reaction. If breaking the reactants' bonds requires more energy than is released as the bonds of the products form, then the chemical reaction absorbs energy. This is what the graph on the right below shows. A chemical reaction that absorbs energy overall is called an endothermic reaction.


The graph on the left shows a reaction system whose bond energy decreases. The graph on the right shows a system whose bond energy increases. So, the overall difference in the bond energies of the reactants and products determines whether the system absorbs or releases energy overall.

You will need to work with your teacher to develop your model. You can model either an exothermic reaction or an endothermic reaction. Materials needed should be readily available to you. After plans for your model are approved, you will need to build and use your model. This will enable you to determine how well your model works. You should then make changes, if necessary so that your model more accurately describes the chemical reaction system.


Part I: Develop a Plan for Your Model (20 points)


1. Research atoms, chemical bonds, chemical reactions, and molecules. As part of your research, find ways that other people have modeled chemical reactions. Summarize your research. Use your summary to develop a plan to create a model showing that the release or absorption of energy from a chemical reaction system depends on the changes in total bond energy. (13 points)


2. Write a brief description of the project you will do. Your description should include these parts: (7 points)

- A descriptive title

- An introduction that describes models and what they are being used for in this project

- A review of scientific research related to your topic

- A step-by-step procedure that describes the methods and materials for developing and using the model

- Any limitations of your model

- A description of how you will evaluate your model

- References