6 Most VSAQ’s of Thermodynamics Chapter in Inter 1st Year Chemistry (TS/AP)

2 Marks

VSAQ-1 : State the first law of the thermodynamics.

The first law of thermodynamics states that energy within a closed system remains constant; it can’t be created or destroyed, but it can change forms. This law is also known as the law of conservation of energy.

VSAQ-2 : State second law of thermodynamics.

The second law of thermodynamics states that heat energy naturally flows from a warmer object to a cooler one, and it’s impossible to create a machine that operates in a continuous cycle while converting all the heat it receives into work without losing some to a colder reservoir. This law implies the existence of entropy, a measure of disorder or randomness in a system, which tends to increase over time in natural processes.

VSAQ-3 : State third law of thermodynamics.

The third law of thermodynamics states that as the temperature of a pure and perfectly crystalline substance approaches absolute zero (0 Kelvin or -273.15°C), the entropy (a measure of disorder) of the substance approaches zero as well. This law implies that a perfectly ordered crystal would have no entropy at absolute zero temperature, which is an idealized limit that cannot be reached in practice.

VSAQ-4 : What is entropy?

Entropy is a measure of the degree of disorder or randomness in a system. It quantifies the number of possible microscopic configurations that a system can have while still maintaining its macroscopic properties. In simpler terms, it represents the amount of chaos or randomness in a system. Entropy tends to increase in natural processes, reflecting the tendency of systems to move from ordered to disordered states, which is a key concept in the second law of thermodynamics.

VSAQ-5 : Give the equation that gives the relationship between ∆U and ∆H.

Relationship between ∆U and ∆H

Equation: The relationship between the change in enthalpy (∆H) and the change in internal energy (∆U) is given by:

$$\Delta H = \Delta U + \Delta nRT$$


  1. ∆H = Change in enthalpy
  2. ∆U = Change in internal energy
  3. ∆n = Change in the number of moles of gas (moles of products – moles of reactants)
  4. R = Universal gas constant
  5. T = Temperature in Kelvin (K)

Explanation: This equation relates the change in enthalpy to the change in internal energy, taking into account the change in the number of moles of gas and the temperature of the system.

VSAQ-6 : What are the ′∆H′sign conventions for exothermic and endothermic reactions?

∆H Sign Conventions for Exothermic and Endothermic Reactions

  1. In an exothermic reaction, ∆H is negative (-). This indicates that the reaction releases heat to its surroundings, resulting in a temperature increase in the surroundings. Exothermic reactions are characterized by a decrease in the enthalpy of the system.
  2. In an endothermic reaction, ∆H is positive (+). This signifies that the reaction absorbs heat from its surroundings, causing a temperature decrease in the surroundings. Endothermic reactions are associated with an increase in the enthalpy of the system.

These sign conventions for ∆H help differentiate between exothermic and endothermic reactions based on whether heat is being released or absorbed during the chemical process.