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Chemical Reactions

Chemical Reactions

Reactions involve the chemical change of atoms and molecules.

Let's start with the idea of a reaction. In chemistry, a reaction happens when two or more molecules interact and the molecules change. That's it. What molecules are they? How do they interact? What happens? The possibilities are infinite.

When you are trying to understand reactions, imagine that you are working with the atoms. Imagine the building blocks are right in front of you on the table, instead of billions of reactions in your beaker. Sometimes we do this using our chemistry toys to help us visualize the movement of the atoms. There are a few key points you should know about chemical reactions:

1. A chemical change must occur. You start with one compound and turn it into another. That's an example of a chemical change. A steel garbage can rusting is a chemical reaction. That rusting happens because the iron (Fe) in the metal combines with oxygen (O2) in the atmosphere.

Hydrogen and oxygen molecules combine to form water in a synthesis reaction. When a refrigerator or air conditioner cools the air, there is no reaction between the air molecules. The change in temperature is a physical change. When you melt an ice cube, it is a physical change. When you put bleach in the washing machine to clean your clothes, a chemical change breaks up the molecules in your stains.

2. We only said molecules at the top of the page. You need to remember that a chemical reaction can happen with anything, just as long as a chemical change occurs (not a physical one). A reaction could include atoms, ions, compounds, or molecules of a single element. If you put pure hydrogen gas (H2) and pure oxygen gas in a room, they might be involved in a reaction to form water (H2O). However, it will be in very very small amounts. If you were to add a spark, those gases would be involved in a violent chemical reaction that would result in a huge explosion (exothermic).

Series of Chemical Reactions 3. Single reactions often happen as part of a larger series of reactions. Take something as simple as moving your arm. The contraction of your muscles requires sugars for energy. Those sugars must first be eaten and then metabolized. You'll also find that proteins need to move in a certain way to make the muscle contract. A whole series (hundreds) of different reactions are needed to make that simple movement happen. In the case of your arm, some changes are physical and some are chemical. In the process of making sugars in a plant, you might have as many as a dozen chemical changes to get through the Calvin cycle and make glucose (C6H12O6) molecules.

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Keywords to Review

Chemical Reaction: The process by which atoms and molecules are manipulated through the creation and destruction of chemical bonds (make them and break them). In a chemical reaction, the process starts with reactants and finishes with products (usually new compounds). Synthesis, decomposition and acid-base are only a few examples of different types of chemical reactions.

Chemical Compound: A compound is a molecule made up of two or more different elements that are linked through chemical bonds. All compounds are molecules, but only molecules with more than one element are compounds. Nitrogen gas (N2) is a molecule while nitrous oxide (N2O) is a molecule and a compound. Chemical reactions are used to create compounds.

Ion: An atom or molecule that has fewer or more electrons than protons. If there are fewer electrons than protons, the substance has a positive charge (protons have a positive charge). If there is an excess of electrons, the substance has a negative charge (electrons have a negative charge). When the number of electrons equals the number of protons, the substance has a neutral charge and is no longer an ion.

Catalyst: A chemical substance that increases the rate of chemical reactions. Catalysts are very specific and are unchanged when the reaction is complete. Their purpose is to lower the activation energy of a single reaction or one reaction is a longer series of reactions. Enzymes in biochemistry are good examples of catalysts.

Catabolism: A process by which chemical compounds are broken down through biological pathways. The ultimate goal of catabolism is to release energy that can be used by an organism to survive. The free energy is often used to create adenosine triphosphate (ATP) which can then be used by cells for other functions. Glycolysis, the chemical breakdown of a glucose molecule, is a good example of catabolism.

Reference Materials

Encyclopædia Britannica:
Rhode Island College:

- Chem4Kids: Rates of Reactions
- Biology4Kids: Scientific Method
- Biology4Kids: Photosynthesis
- Biology4Kids: Phagocytosis
- Biology4Kids: Homeostasis
- Geography4Kids: Biogeochemical Cycles
- Geography4Kids: Food Chains & Webs
- Geography4Kids: Temperature Scales
- Physics4Kids: Thermodynamics
- Physics4Kids: Thermodynamic Laws

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