Q12.11P - Chemistry: Molecular Nature Of Matter And Change

Question

Describe the changes (if any) in potential energy and in kinetic energy among the molecules when gaseous ${\mathbf{PCl}}_{\mathbf{3}}$ condenses to a liquid at a fixed temperature.

Step-by-Step Solution

Answer

When gaseous ${\mathrm{PCl}}_3$ converts into the liquid form, the potential energy of the molecules increases whereas the kinetic energy decrease at a fixed temperature.

Step1: Relative magnitude of intermolecular forces

The intermolecular forces of attraction are comparatively higher in liquids than the solids.

Due to this relative magnitude of the intermolecular forces, and as per the law of conservation of energy the energy of molecules is distributed in kinetic energy and potential energy.

Step2: Potential and kinetic energy

As the gaseous molecules have low intermolecular attraction, their potential energy is less than liquids and as they are free to move randomly their kinetic energy is high at a fixed temperature.

 

Hence, when gaseous  converts into the liquid form at a constant temperature, the potential energy increases and the kinetic energy decrease during the process.

Step3: Conservation of energy

In various phases, the law of conservation of energy is always obeyed, the total energy is the sum of translational, rotational and vibrational energy.

In the gaseous phase, the translational and rotational energy component is more whereas in the solid phase the vibrational energy component is higher.