The first excited state of a particular atom in a gas is 5.2 eV above the ground state. A moving electron collides with one of these atoms, and excites the atom to its first excited state. Immediately after the collision the kinetic energy of the electron is 2.2 eV. What was the kinetic energy of the electron just before the collision?

7.4eV

Explanation:

We are given tha

Energy of a particular atom in a gas in the first excited state=5.2 eV

Kinetic energy of the electron after collision=K. E=2.2 eV

We have to find the kinetic energy of the electron just before the collision.

We know that energy transferred from one particle to other atom.

By conservation law of energy

Kinetic energy of electron just before the collision=K. E of electron after collision + energy of atom in a gas in the first excited state

Kinetic energy of electron just before the collision=2.2e V+5.2 eV=7.4eV

Hence, the kinetic energy of electron just before the collision=7.4 eV