H2 (g) + I2 (g) ⇌ 2 HI(g) Kc = 54.3 at 430 °C . What will be the concentrations of all species at equilibrium at this temperature if we start with the following initial concentrations: [H2 ] =0.00623 M, [I2 ] = 0.00414 M, and [HI] = 0.0424 M?

Respuesta :

Answer:

[H₂]  = 6.74×10⁻³ M

[I₂]  = 4.65×10⁻³ M

[HI] = 0.0413 M

Explanation:

The equilibrium is:

H₂(g) + I₂(g) ⇌ 2 HI(g)

Expression for Kc = [HI]² / [H₂] .  [I₂]            54.3

We analyse the equation:

                 H₂(g)      +     I₂(g)      ⇌      2 HI(g)

Initially   0.00623      0.00414              0.0424

React            x                  x                        2x

x amount has reacted, therefore by stoichiometry 2x has been added to the HI, that we have in the beginning.

Eq         0.00623-x    0.00414-x             0.0424+2x

We make the expression for Kc:

Kc = (0.0424+2x)² / (0.00623-x) . (0.00414-x)  = 54.3

This is quadractic funcion:

54.3 = (1.79×10⁻³ + 0.1696x + 4x²) / (2.58×10⁻⁵- 0.01037x + x²)          

54.3 (2.58×10⁻⁵- 0.01037x + x²) = 1.79×10⁻³ + 0.1696x + 4x²

1.40×10⁻³- 0.563x + 54.3x² = 1.79×10⁻³ + 0.1696x + 4x²

-3.89×10⁻⁴ - 0.7326x +50.3x² = 0 → a = 50.3 ; b= - 0.7326 ; c = -3.89×10⁻⁴

Quadratic formula = (-b +- √(b² + 4ac))/ (2a)

x₁ = 0.015

x₂ = -5.13×10⁻⁴  . We choose x₂ as x₁ give us negative concentrations

[H₂] = 0.00623 - (-5.13×10⁻⁴) = 6.74×10⁻³ M

[I₂] = 0.00414 - (-5.13×10⁻⁴) = 4.65×10⁻ M

[HI] = 0.0424+2(-5.13×10⁻⁴) = 0.0413 M

The concentration will be "0.00663 M, 0.00454 M, and 0.0416 M".

Concentration and Equilibrium

According to the question,

Value of  Kc = 54.3

Temperature = 430°C

The equation will be:

→ H₂ (g) + I₂ (g) [tex]\rightleftharpoons[/tex] 2HI (g)

Here,

Initial concentration,

[H2] =0.00623 M

[I2] = 0.00414 M

[HI] = 0.0424 M

Value of  Kc = 54.3

We know the relation,

→ [tex]K_c[/tex] = [tex]\frac{[HI]^2}{[H_2][I_2]}[/tex]

By substituting the values,

54.3 = [tex]\frac{(0.0424+2x)^2}{(0.00623-x)(0.00414-x)}[/tex]

54.3x² + 0.0014 - 0.563x = 0.0017 + 4x² + 0.1696x

50.3x² - 0.732x - 0.0003 = 0  

                                       x = -0.0004

Now,

[H₂] equilibrium = 0.00623 + 0.0004

                          = 0.00663 M

[I₂] equilibrium = 0.00414 + 0.0004

                        = 0.00454 M

[HI] equilibrium = 0.0424 - 2(0.0004)

                         = 0.0416 M

Thus the response above is right.

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