In a study of the conversion of methane to other fuels, a chemical engineer mixes gaseous CH4 and H2O in a 0.32-L flask at 1200 K. At equilibrium the flask contains 0.028 mol of CO, 0.084 mol of H2, and 0.045 mol CH4. What is [H2O] at equilibrium if Kc at this temperature is 0.26

[H2O] = 0.0434 M

Explanation:

Step 1: Data given

Moles CH4 = 0.045 moles

Moles CO = 0.028 moles

Moles H2 = 0.084 moles

Volume = 0.32 L

Temperature = 1200 K

Kc = 0.26

Step 2: The balanced equation

CH4 (g) + H2O (g) ⇆ CO (g) + 3H2 (g)

Step 3: Calculate molarity at the equilibrium

[CH4] = 0.045 moles / 0.32 L = 0.141 M

[H2O] = ?

[CO] = 0.028 moles / 0.32 L = 0.0875 M

[H2] = 0.084 moles / 0.32 L = 0.263 M

Step 4: Calculate [H2O]

Kc = 0.26 = [CO][H2]³/[CH4][H2O]

0.26 = 0.0875*0.263³ / 0.141*[H2O]

0.26 = 0.0015917516125 / 0.141*[H2O]

0.141*[H2O] = 0.0015917516125 / 0.26 = 0.006122

[H2O] = 0.0434 M