What Is a Chemical Reaction?
A chemical reaction is the process in which two or more substances interact at the atomic or molecular level, lose their original structures completely, have their chemical bonds broken, and form substances with new physical and chemical properties.
What Changes as a Result of a Chemical Reaction?
Chemical reactions are transformation processes in which matter is rearranged at the atomic or molecular level and new compounds or elements are formed. Various physical and chemical changes take place during this process:
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Properties of the Substance: The chemical and physical properties of the substances entering the reaction (color, odor, melting point, solubility, flammability) change completely, and the distinctive properties of the new products emerge.
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Chemical Bonds: During the reaction, the existing chemical bonds between the atoms break and new bonds form in different combinations. This turns the substance into a completely different structure at the molecular level.
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Energy Change: Energy may be released during a chemical reaction (exothermic reactions) or energy may be absorbed (endothermic reactions). This energy change is usually observed as heat, light, or electrical energy.
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Mass and Distribution of Matter: The mass of the reactants is conserved, while the atoms combine in different arrangements and form new substances.
What Are the Substances Formed by a Chemical Reaction Called?
When a chemical reaction takes place, the substances that entered the reaction at the start are transformed and form new compounds or elements. These new substances that emerge at the end of the reaction are called products. The chemical and physical properties of the products differ from those of the reactants.
Newly Formed Substances Do Not Show Their Former Properties
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During a chemical reaction, electrons are transferred or shared between the atoms.
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This leads the atoms to form new bonds and produces a completely different molecule or compound.
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Because the internal structure of the newly formed compound differs from that of the former substances, its physical and chemical properties also differ.
Electron Configuration and Chemical Properties
Electron configuration determines chemical properties, because the electrons of an atom determine whether it will enter a reaction, how it will bond, and which kinds of substances it will interact with.
Exothermic and Endothermic Reactions
Exothermic reaction
These are chemical reactions that give off heat to their surroundings. The surroundings warm up.
- CH4 + 2O2 → CO2 + 2H2O + heat
- 2H2 + O2 → 2H2O + heat
- C + O2 → CO2 + heat
- HCl + NaOH → NaCl + H2O + heat
- 2Mg + O2 → 2MgO + heat
Endothermic reaction
These are chemical reactions that take heat from their surroundings in order to proceed. The surroundings cool down.
- 2H2O + heat → 2H2 + O2
- CaCO3 + heat → CaO + CO2
- 2KClO3 + heat → 2KCl + 3O2
- NH4Cl + heat → NH3 + HCl
- N2 + O2 + heat → 2NO
Polymerization Reactions
A polymerization reaction is the linking of small molecules (monomers) to one another to form long-chain large molecules (polymers). Most of the plastics, nylon, and rubber we use in daily life are obtained through these reactions.
General representation:
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n (monomer) → polymer
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n CH2=CH2 → (–CH2–CH2–)n (Polyethylene)
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n CH2=CHCl → (–CH2–CHCl–)n (PVC)
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n CF2=CF2 → (–CF2–CF2–)n (Teflon)
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n CH2=CH–CH3 → (–CH2–CH(CH3)–)n (Polypropylene)
Hydrolysis Reactions
A hydrolysis reaction is the splitting of a compound into smaller molecules by reacting with water.
Properties of the Hydrolysis Reaction
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Water is used
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Large molecule → smaller molecules
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Bonds are broken with the help of water
Protein + (n – 1) H2O → n (Amino acid)
Carbohydrate + (n – 1) H2O → n (Monosaccharide)
Fat + H2O → Fatty acid + Glycerol
Sucrose + H2O → Glucose + Fructose
Starch + n H2O → n Glucose
What Is a Chemiluminescence Reaction?
Chemiluminescence is the emission of light from the medium during a chemical reaction. It comes about through a change in the energy levels of the electrons of the atoms. It is widely used both for its striking effect and for its ability to reveal the presence of certain substances.
What Are the Types of Chemical Reaction?
Chemical reactions are processes that rearrange matter at the atomic and molecular level and bring about the formation of new substances. They can be grouped into different categories according to their formation mechanisms and the way they take place. The most common types of chemical reaction are the following:
1. Synthesis (Combination) Reactions
These are reactions in which two or more simple substances combine and form a more complex compound.
General equation: A + B → AB
Example: 2H₂ + O₂ → 2H₂O (formation of water)
2. Decomposition (Analysis) Reactions
These are reactions in which a compound separates into the simpler components or elements that make it up.
General equation: AB → A + B
Example: 2H₂O → 2H₂ + O₂ (electrolysis of water)
3. Displacement (Single Displacement) Reactions
These are reactions in which one element drives another element out of a compound.
General equation: A + BC → AC + B
Example: Zn + CuSO₄ → ZnSO₄ + Cu (zinc reacts with copper sulfate solution and releases copper)
4. Double Displacement Reactions
These are reactions in which the ions of two compounds change places with one another. They usually take the form of precipitate formation, gas evolution, or neutralization reactions.
General equation: AB + CD → AD + CB
Example: AgNO₃ + NaCl → AgCl (precipitate) + NaNO₃
5. Combustion Reactions
These are reactions in which a substance reacts with oxygen and releases heat and light. Water and carbon dioxide are usually formed when hydrocarbons and other organic compounds react with oxygen.
General equation: CₓHᵧ + O₂ → CO₂ + H₂O + Energy
Example: CH₄ + 2O₂ → CO₂ + 2H₂O + Heat (combustion of methane gas)
6. Acid-Base (Neutralization) Reactions
Reactions between acids and bases usually form a salt and water.
General equation: Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H₂O
7. Precipitation Reactions
These are reactions in which the ions present in a solution combine and form an insoluble solid substance (a precipitate).
Example: BaCl₂ + Na₂SO₄ → BaSO₄ (precipitate) + 2NaCl
8. Oxidation-Reduction (Redox) Reactions
These are reactions based on the transfer of electrons. Oxidation is the loss of electrons by an element; reduction is the gain of electrons.
Example: Fe + O₂ → Fe₂O₃ (rusting of iron)
Chemical reactions form the basis of many processes in nature and in industry. Understanding these different reaction types offers important applications in many fields such as chemical engineering, environmental science, and biochemistry.
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Author:
Industrial Design Engineer