Question

2. Energy cost of plasma generation of NO, NO2, and NO3 in air (or air bubble) is about 20 eV per N-atom. 100 W plasma system has been treating 2L of water during 60 min. Assuming that all plasma generated nitrogen oxides have been absorbed in water, calculate number of moles per liter of the nitrogen compounds in the produced water solution.

Answer 1

Answer:

0.0933 moles/Litre

Explanation:

We assume that the number of moles of N- used is equal to the number of moles of Nitrogen containing compounds that are generated due to the fact that the nitrogen containing compound that are produced contain only one nitrogen in each atom. As such, finding the amount of nitrogen used up explains the amount of compound formed. This can  be expressed as follows:

Energy cost = $\frac{20ev}{N- atom}$

Given that:

Energy = 100 W for 60 minutes

100 W = 100 J/s

           = 100 J/s × (60 × 60) seconds

           = 3.6 × 10⁵ J

Let now convert 3.6 × 10⁵ J to eV; we have:

= ( 3.6 × 10⁵  × 6.242 × 10¹⁸ )eV

= 2.247 × 10²⁴ eV

So, number of N-atom used up to form compounds will now be:

= 2.247 × 10²⁴ eV  × $\frac{1}{20eV} N-atom$

= 1.123 × 10²³ N-atom

To moles; we have:

= $\frac {1.123*10^{23}} {6.023*10^{23}}$

= 0.186 moles

However, we are expected to leave our answer in concentration (i.e in moles/L)

since we are given 2L

So;   0.186 moles ⇒   $\frac{0.186 moles}{2 Litre}$

= 0.0933 moles/Litre