Learning About Chemical Reactions For Students

Do you ever wonder how a nail becomes rusty after it is exposed to water, or how water can turn from ice to steam when heat is applied? Chemical reactions occur every day and most chemical reactions are natural occurrences at home or at school. They are reactions that occur between two opposing substances that when combined change each other’s molecular structure. Chemical reaction rates can be increased or decreased by various factors such as concentration, temperature, surface area, and catalysts or inhibitors. The four types of chemical reactions that can occur are synthesis, decomposition, replacement, and ionic.

What is a Chemical Reaction?

All substances are made up of tiny molecules. A molecule is made up of a group of tiny atoms. A chemical reaction is when there is a change in the molecular make up of a material. This can happen when two substances are combined to create a new substance. This is different from a physical change in a substance because when a material has a physical change the original item is still able to be recovered. The atoms are still in the same exact order as they were prior to the physical change. A substance that has a chemical change cannot be changed back into its original form because the tiny atoms that make up the substance have been rearranged into a different order.

Rates of Reactions

In a chemical reaction, all the molecules have to collide with one another before the reaction is complete. The rate at which a chemical reaction occurs or the amount of time chemical it takes for reactants to be used up is called the rate of reaction. Depending on how fast the molecules are creating chemical “collisions” the speed of the chemical reaction can change. For a complete chemical reaction, all particles must have collided with opposing particles to create a “new” substance.

There are four things that can either speed up or slow down a chemical reaction once the two substances have been combined: concentration, temperature, surface area, and catalysts or inhibitors. Concentration, temperature, surface area, and catalysts or inhibitors play a vital role in a chemical reaction. The more heavily concentrated the number of particles within a chemical reaction, the faster the amount of collisions will occur. The higher the temperature in a chemical reaction also helps to increase the speed of the movement of the particles. This also causes an increase in chemical collisions. Surface area helps to increase the reaction rate. This is caused by the amount of space for the movement of the particles. If there is little space then there is a greater rate at which the particles collide, however if there is too much space in relation to the number of particles then the reaction rate will take longer. A catalyst works by increasing the speed at which the reaction rate occurs, but unlike the opposing substance that helps to create a chemical reaction, it does not change form in a chemical reaction.

Catalysts & Inhibitors

Sometimes chemical reactions need a boost to speed up the process. This boost is called a catalyst and can be added to a chemical reaction without changing the process or being changed in the process. An example of a catalyst is salt being added to water. Without salt, water can take a longer time to boil, but when salt is added the salt increases the rate at which the water will begin to boil. An inhibitor is also an extra ingredient that does not change form when added to a chemical reaction, but unlike a catalyst it can slow down or even prevent the reaction from happening. An inhibitor works by combining with one of the substances used in a chemical reaction, so that the reaction cannot take place. An example of an inhibitor is a food preservative such as lemon juice. Lemon juice can be added to fruit to keep fruit from turning brown from being exposed to the air.

Types & Examples of Chemical Reactions

Chemical reactions are grouped into four basic types: synthesis; decomposition; replacement; ionic. In a synthesis reaction, the two opposing substances that were used in the chemical reaction now are combined to create a new substance. An example of a synthesis reaction is A + B is equal to AB or sodium plus chloride makes sodium chloride. A chemical reaction using decomposition breaks apart the original substance to form the two opposing substances. An example is when hydrogen peroxide can be broken apart into hydrogen and oxygen using magnesium dioxide. An example of a decomposition reaction is AB is equal to A + B. A replacement reaction involves the “replacement” or rearranging of molecules used from one substance to another. An example of a replacement chemical reaction is AB + C forming into A + BC. An ionic chemical reaction involves two opposing substances that form a precipitate substance when combined. One example of an ionic reaction is mixing sodium chloride and silver nitrate to form the precipitate silver chloride.

Chemical reactions are changes that occur when the makeup of a substance is changed and cannot be formed back into its original state. The rate of reaction at which a chemical reaction can occur is dependent upon four variables to determine the rate of reaction: concentration, temperature, surface area and catalysts or inhibitors. Catalysts or inhibitors can increase or decrease the rate of reaction, but do not change the process of the chemical reaction. Chemical reactions are categorized into four main groups: synthesis, decomposition, replacement, and ionic. Chemical reactions when simplified are able to be easily understood, and examples of chemical reactions can be seen every day whether at home or at school.

 

Written by Grace Ann Stanford

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