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A chemical reaction is a process that involves rearrangement of the molecular or ionic structure of a substance. This involves breaking or formation of bonds between the atoms or ions.

This course covers examples of chemical reaction , types of chemical bonds, and types of chemical reaction.

When we hear the word chemistry, we envision yourselves in a lab and using laboratory equipment. But if we look closely around us, there are several chemical reactions occurring that form a large part of your daily life.

Rusting, cooking, digestion, photosynthesis, and burning of fossil fuels are a few examples. A chemical reaction is accompanied by change in temperature, color (Figure 1), and/or precipitate formation.

Figure 1. A chemical reaction showing color change
Figure 1. A chemical reaction showing color change

Chemical Reactions in Everyday Life

  • Process of digestion– As food enters our mouth, several different chemical reactions start in our digestive tract. Several enzymes undergo chemical reactions for the digestion (Figure 2), and assimilation of the food.
Figure 2. Digestion of Protein. Enzymes (proteases and peptidases) are digestion breaks the protein into smaller peptide chains and into single amino acids, which are absorbed into the blood
Figure 2. Digestion of Protein
  • Food preservation- Several preservatives used not only prohibit the growth of bacteria, virus, fungi but also hinder the oxidation of fats that make foods rancid (Figure 3). The most used preservatives are sodium benzoate, sorbic acid, potassium sorbate, calcium sorbate, sodium sorbate, propionic acid, and the salts of nitrous acid.
Figure 3. Food preservation
Figure 3. Food preservation
  • Baking- What is the reason cake, biscuit and bread feels fluffy? Addition of baking soda to food items leads to the production of carbon dioxide (CO2) causing the foods to rise (Figure 4). This process is called chemical leavening.
Figure 4. Fluffy biscuits
Figure 4. Fluffy biscuits
  • Cleaning hands or clothes- The cleaning action of soap is based on its ability to act as an emulsifying agent. Soaps are fatty acids salts of sodium or potassium, produced by a chemical reaction called saponification. The cleansing action of soaps results from their ability to lower the surface tension of water, to emulsify oil or grease and to hold them in a suspension in water.
  • Photosynthesis- Plants produce food by the process of photosynthesis. The chemical reaction involved in photosynthesis (Figure 5) is shown below:
Figure 5. A chemical reaction involved in photosynthesis
Figure 5. A chemical reaction involved in photosynthesis
  • Chemistry of emotion and body composition- There are chemical reactions associated with feeling happy, sad, relaxed, or stressed. It is because of the chemical messengers called neurotransmitters released in the brain. There are biochemical reactions involved in nerve signaling (Figure 6), muscle functioning, formation of bone and many other processes of life.
Figure 6. Signal transmission at a chemical synapse
Figure 6. Signal transmission at a chemical synapse

Types of Bonds

Molecules are formed when two or more atoms participate in chemical bonding. The stability of a molecule is dependent on the strength of the chemical bonds holding the atoms together. There are three main types of chemical bonds: covalent, ionic, and metallic.

Covalent Bonds

Covalent bonds occur when electrons are shared between 2 atoms and the bond is classified as polar or nonpolar. Pauling Units (PU) are used to measure the electronegativity of a bond. This type of chemical bonding is found in water (Figure 7) and often in organic compounds.

Figure 7. Covalent bond for example water molecule (H2O)
Figure 7. Covalent bond for example water molecule (H2O)
  • A polar covalent bond usually involves 2 different types of atoms and occurs when one atom has a stronger pull on the electron, or a greater electronegativity. For example, ammonia (Figure 8) is formed by polar covalent bonding between nitrogen and hydrogen. The stronger atom will have a slightly negative charge and the other atom(s) will be slightly positive which results in poles on the molecule. Polar bonds have a measurement of 0.5-1.9 PU.
Figure 8. Polar covalent bonding in methane
Figure 8. Polar covalent bonding in methane
  • A nonpolar covalent bond usually occurs between 2 atoms of the same element, which pull equally on the electron. Methane is formed by non polar covalent bonding between carbon and hydrogen (Figure 9). Non-polar bonds have a measurement of <0.5PU.
Figure 9. Non polar covalent bonding in methane
Figure 9. Non polar covalent bonding in methane

Ionic Bonds

Ionic bonds occur when one atom gives up one or more electrons and another atom accepts the electron. These oppositely charged ions attract each other resulting in a bond (Figure 10).

  • The positively charged atom is called a cation and is usually a metal.
  • The negatively charged atom is an anion and is usually a non-metal.
Figure 10. Sodium Chloride (NaCl) is formed by ionic bond
Figure 10. Sodium Chloride (NaCl) is formed by ionic bond

Metallic Bonds

Metallic bonds occur between 2 metal atoms of the same or different elements. The metals give up electrons which causes them to have a positive charge. The electrons hover near the metals and are all attracted to the same area, which basically bonds them together. These floating electrons are what allows metals to conduct electricity well and be malleable.