Synthesis Reactions
A chemical reaction occurs when atoms, ions, molecules, or compounds interact either to form or to break chemical bonds. Reactants are substances that enter into a chemical reaction, whereas the substances that result from the chemical reaction are called products.
A synthesis reaction is when two or more reactants chemically combine to form a new and larger product. The synthesis reactions occurring in the body are collectively referred to as anabolism. These reactions produce the molecules characteristic of life, such as ATP, proteins, carbohydrates, lipids, and nucleic acids. Some conditions of the body such as growth, maintenance, and repair could not take place without anabolic reactions. Synthesis reactions in which water is a product are called dehydration (water out) reactions.
Decomposition Reactions
A decomposition reaction is the reverse of a synthesis reaction—a larger reactant is chemically broken down into two or more smaller products. The decomposition reactions occurring in the body are collectively called catabolism. They include the digestion of food molecules in the intestine and within cells, the breakdown of fat stores, and the breakdown of foreign matter and microorganisms in certain blood cells that protect the body. All of the anabolic and catabolic reactions in the body are collectively defined as metabolism. An example of a decomposition reaction is the breakdown of a disaccharide (a type of carbohydrate) into glucose molecules. Note that this reaction requires that water be split into two parts and that each part be contributed to one of the new glucose molecules. Reactions that use water in this manner are called hydrolysis (water dissolution) reactions.
Reversible Reactions
Some chemical reactions are reversible. In a reversible reaction, the reaction can run in the opposite direction, so that the products are converted back to the original reactants. When the rate of product formation is equal to the rate of the reverse reaction, the reaction system is said to be at equilibrium. At equilibrium, the number of reactants relative to the number of products remains constant.
Oxidation-Reduction Reactions
Chemical reactions that result from the exchange of electrons between the reactants are called oxidation-reduction reactions. When sodium and chlorine react to form sodium chloride, the sodium atom loses an electron and the chlorine atom gains an electron. The loss of an electron by an atom is called oxidation, and the gain of an electron is called reduction. The transfer of the electron can be complete, resulting in an ionic bond, or it can be partial, resulting in a covalent bond. Because one atom partially or completely loses an electron and another atom gains that electron, these reactions are called oxidation-reduction reactions. Synthesis and decomposition reactions can be oxidation-reduction reactions. Thus, a chemical reaction can be described in more than one way.
Energy
Energy is the ability to do work—that is, to move matter. Energy can be subdivided into potential energy and kinetic energy. Potential energy is stored energy that available to do work but is not doing so. Kinetic energy is the form of energy that is being used to do work, it is the energy of motion to move matter. A ball held at arm’s length above the floor has potential energy. No energy is expended as long as the ball does not move. However, if the ball is released and falls toward the floor, it has kinetic energy.
Potential and kinetic energy exist in many different forms. Here we consider mechanical, chemical, and heat energy. Mechanical energy is the energy results from the position or movement of objects. Many of the activities of the human body, such as moving a limb, breathing, and circulating blood, involve mechanical energy.
Chemical Energy
Chemical energy is a form of potential energy stored within the chemical bonds of a substance. In any chemical reaction, the potential energy in the chemical bonds of the reactants can be compared with the potential energy in the chemical bonds of the products. If the potential energy in the reactants is less than that in the products, energy must be supplied for the reaction to occur.
 |
(a)-Energy is released as a result of the breakdown of ATP.
(b)-The input of energy is required for the synthesis of ATP.
| |
|
Heat Energy
Heat energy is a form of energy that flows from a hotter object to a cooler object. Temperature is a measure of how hot or cold a substance is in respect to another substance. All other forms of energy can be converted into heat energy. For example, when a moving object comes to rest, its kinetic energy is converted into heat energy by friction. Some of the potential energy of chemical bonds is released as heat energy during chemical reactions. Human body temperature is maintained by heat produced as a by-product of chemical reactions.
Click here to read about: The Chemistry of Life
Comments
Post a Comment
សំណួរ ឬយោបល់ផ្សេងៗ