Basic Chemistry: The Concept of Equilibrium, the Context of Chemistry and Energy

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Equilibrium and Energy -Boltzmann’s Population Factor, Arrhenius Equation|Chemistry|NEET|NSO

Learning Outcomes

After studying this lesson, you shall be able to:

  • Equilibrium

  • Energy


  • Although the concept of equilibrium is widely used across sciences, in the context of chemistry, chemical reaction is said to be in equilibrium when the reactants and products are in a constant ratio.

  • The forward reaction and the reverse reactions occur at the same rate when a system is in equilibrium.



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  • A system of chemical substances at equilibrium even though having an unchanging composition is most often not static.

  • Molecules of the substances continue to react with one another thus giving rise to a dynamic equilibrium.

  • Thus, the concept describes the state in which the parameters such as chemical composition remains unchanged over time.


  • In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure.

  • Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved.

  • Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus, the products of a reaction may have more or less energy than the reactants.

  • A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state.

  • in the case of endergonic reactions, the situation is reverse.

  • A reaction is said to be exothermic if the reaction releases heat to the surroundings.

  • in the case of endothermic reactions, the reaction absorbs heat from the surroundings.

  • Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy.

Energy scale

Energy Scale

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  • The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the

  • Boltzmann’s population factor - that is the probability of molecule to have energy greater than or equal to Eat the given temperature T.

  • This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation.

  • The activation energy necessary for a chemical reaction can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.


1. What is the representation of a reversible reaction?

  1. single arrow

  2. double arrow

  3. Bar

  4. None of the above

Answer: double arrow

2. What is the term used for a state of a chemical reaction in which forward and reverse reactions take place at the same rate?

  1. chemical equilibrium

  2. Stable reaction

  3. reversible reaction

  4. forward reaction

Answer: A. chemical equilibrium