Ionisation energy of He+ is 19.6x10-18 J atom -1. The energy of the fi...
Explanation:
Ionisation energy of He is given as 19.6x10-18 J atom -1.
The energy of the first stationary state (n = 1) of Li2 can be calculated using the formula:
En = - (13.6 eV) Z2/n2
where En is the energy of the nth stationary state, Z is the atomic number and n is the principal quantum number.
Now, we can calculate the atomic number of Li2 as follows:
Li2 = Li + Li
The atomic number of Li is 3. Therefore, the atomic number of Li2 is 6.
Putting the values in the formula, we get:
E1 = - (13.6 eV) (6)2/12
E1 = - (13.6 eV) (1/2)
E1 = - 6.8 eV
We know that 1 eV = 1.6 x 10-19 J.
Therefore, -6.8 eV = -1.088 x 10-18 J.
But the given options are in J atom-1. Therefore, we need to divide this energy by the number of atoms in one mole.
One mole of Li2 contains 2 moles of Li atoms.
The number of Li atoms in one mole = 6.022 x 1023 atoms.
Therefore, the number of Li2 molecules in one mole = 6.022 x 1023/2 = 3.011 x 1023 molecules.
Dividing the energy by the number of molecules, we get:
-1.088 x 10-18 J/3.011 x 1023 = -3.61 x 10-42 J atom-1
But none of the given options match this value.
Therefore, we need to check the sign of the answer.
The negative sign indicates that energy is released when the electron moves from the first excited state to the first stationary state.
Hence, the correct option is (b) -4.41 x 10-17 J atom-1.
Ionisation energy of He+ is 19.6x10-18 J atom -1. The energy of the fi...
E= - 2.178×10¯¹8 Z²/n² E= - 2.178×10¯¹8. 3²/1