Question

The ionisation energy of gold is 890.1 kJ/mol. Is light with a wavelength of 225 nm capable of ionising a gold atom ?

Answer 1

No it is not.

Ionisation energy refers to:

`Au_((g))rarrAu_((g))^++e`

1 mole requires `890.1"kJ" =8.901xx10^5"J"`

1 atom requires `(8.901xx10^5)/(6.02xx10^(23))"J"`

`=1.478xx10^(-18)"J"`

To find the energy of the photon we use:

`E=hf`

To get the frequency of the photon we use :

`c=flambda`

`c` is the speed of light `=3xx10^(8)"m/s"`

So `f=c/lambda=(3xx10^8)/(225xx10^(-9)`

`f=1.333xx10^(15)s^(-1)`

So `E=6.63xx10^(-34)xx1.333xx10^(15)"J"`

`E=8.84xx10^(-19)"J"`

So you can see that this falls short of the energy required to ionise the gold atom as it is less than `1.487xx10^(-18)"J"`.