Answer: The concentration of water at equilibrium is 0.3677 mol/L
Step-by-step explanation:
Equilibrium constant in terms of concentration is defined as the ratio of concentration of products to the concentration of reactants each raised to the power their stoichiometric coefficients. It is represented by

For a general chemical reaction:

The
is written as:
![K_(c)=([C]^c[D]^d)/([A]^a[B]^b)](https://img.qammunity.org/2020/formulas/chemistry/high-school/13aayk47tkvc79ferxww1rmrj9bfzrdqu4.png)
The chemical equation for the conversion of methane to carbon monoxide and hydrogen gas follows:

The
is represented as:
....(1)
To calculate the concentration, we use the equation:

We are given:
![[CO]=(0.145mol)/(0.379L)=0.383mol/L](https://img.qammunity.org/2020/formulas/chemistry/college/8xkka1l5c4o5dw60l1gflbjk0uxotdqxlp.png)
![[H_2]=(0.218mol)/(0.379L)=0.575mol/L](https://img.qammunity.org/2020/formulas/chemistry/college/j2i6o8n7jm91w6jban8wy3vd6n6ui2rrkr.png)
![[CH_4]=(0.25mol)/(0.379L)=0.660mol/L](https://img.qammunity.org/2020/formulas/chemistry/college/m9fsrzgvjhluhtx7zgina7fiibqucltxjz.png)

Putting values in equation 1, we get:
![0.30=((0.575)^3* 0.383)/(0.660* [H_2O])](https://img.qammunity.org/2020/formulas/chemistry/college/cq09sthrprssj6swf7r1bror4swpsbdgw3.png)
![[H_2O]=((0.575)^3* 0.383)/(0.660* 0.30)=0.3677](https://img.qammunity.org/2020/formulas/chemistry/college/w1ymav18ntupbkxo4mcc9pejd2ihi6ky8z.png)
Hence, the concentration of water at equilibrium is 0.3677 mol/L