Question

2. A reaction vessel is charged with hydrogen iodide, which partially decomposes to molecular hydrogen and iodine:2HI (g) H2(g) + I2(g)When the system comes to equilibrium at 425 °C, PHI = 0.794 atm, and PH2 = PI2 = 0.0685 atm. The value of Kp at this temperature is ________.

Answer 1

Answer:

The value of Kp at this temperature is 7.44*10⁻³

Explanation:

Chemical equilibrium is established when there are two opposite reactions that take place simultaneously at the same speed.

For the general chemical equation for a homogeneous gas phase system:

aA + bB ⇔ cC + dD

where a, b, c and d are the stoichiometric coefficients of compounds A, B, C and D, the equilibrium constant Kp is determined by the following expression:

$Kp=\frac{P_{C} ^{c} *P_{D} ^{d} }{P_{A} ^{a} *P_{B} ^{b} }$

Where Px is the partial pressure of each of the components once equilibrium has been reached and they are expressed in atmospheres. The equilibrium constant Kp depends solely on temperature and is dimensionless.

In the case of the reaction:

2 HI (g) ⇔ H₂ (g) + I₂ (g)

the equilibrium constant Kp is determined by the following expression:

$Kp=\frac{P_{H_{2} } *P_{I_{2} } }{P_{HI} ^{2} }$

The system comes to equilibrium at 425 °C, and

• PHI = 0.794 atm
• PH2 = 0.0685 atm
• PI2 = 0.0685 atm

Replacing:

$Kp=\frac{0.0685*0.0685}{0.794^{2} }$

Kp=7.44*10⁻³

The value of Kp at this temperature is 7.44*10⁻³