Hydrogen sulfide decomposes according to the following reaction, for which Kc=9.30E-8 at 700 degrees Celsius. 2 H2S(g) --> 2 H2(g) + S2(g) If 0.29 moles of H2S is placed in a 3.0-L container, What is the equilibrium concentration of H2(g) at 700 degrees Celsius?

1 Answer
Jul 12, 2014

The equilibrium concentration of "H"_2H2 is 0.012 mol/L.

Explanation:

Step 1. Calculate the initial concentrations

["H"_2"S"]_0 = "0.29 mol"/"3.0 L" = "0.0967 mol/L"[H2S]0=0.29 mol3.0 L=0.0967 mol/L

Step 2. Write the balanced equation and set up an ICE table.

color(white)(mmmmmmm)"2H"_2"S"color(white)(m) ⇌color(white)(m) "2H"_2 + "S"_2mmmmmmm2H2Smm2H2+S2
"I/mol·L"^"-1":color(white)(m) "0.096 67" color(white)(mmmm)0 color(white)(mm)0I/mol⋅L-1:m0.096 67mmmm0mm0
"C/mol·L"^"-1":color(white)(mm) "-"2xcolor(white)(mmmm) "+2"xcolor(white)(m) "+"xC/mol⋅L-1:mm-2xmmmm+2xm+x
"E/mol·L"^"-1": "0.096 67 - 2"xcolor(white)(lmm) 2xcolor(white)(ml) xE/mol⋅L-1:0.096 67 - 2xlmm2xmlx

Write the K_"c"Kc expression and solve for xx.

K_"c" = (["H"_2]^2["S"_2])/["H"_2"S"]^2 = 9.30 × 10^"-8"Kc=[H2]2[S2][H2S]2=9.30×10-8

((2x)^2×x)/(("0.096 67" – 2x)^2) = 9.30 × 10^"-8"(2x)2×x(0.096 672x)2=9.30×10-8

0.09667/(9.30 ×10^"-8") = 1 × 10^"-6" > 4000.096679.30×10-8=1×10-6>400. ∴x ≪ "0.099 67"x0.099 67

(4x^3)/"0.096 67"^2 = 9.30 × 10^"-8"4x30.096 672=9.30×10-8

4x^3 = "0.096 67"^2 × 9.30 × 10^"-8" = 8.691 × 10^"-10"4x3=0.096 672×9.30×10-8=8.691×10-10

x^3 = 2.173 × 10^"-10"x3=2.173×10-10

x = 6.012 × 10^"-4"x=6.012×10-4

["H"_2] = 2xcolor(white)(l) "mol/L" = 2 × 6.012 × 10^"-4"color(white)(l) "mol/L" = "0.0012 mol/L"[H2]=2xlmol/L=2×6.012×10-4lmol/L=0.0012 mol/L