Chemistry

Problem

For the gas–phase equilibrium

H_2(g)+I_2(g)\rightleftharpoons 2HI(g)

at 700 K,

K_p = 51

. A sealed container at 700 K contains

P_{H_2}=2.0\,\text{atm}

P_{I_2}=1.5\,\text{atm}

, and

P_{HI}=10\,\text{atm}

. Predict whether the partial pressure of

HI

will increase or decrease as the system moves toward equilibrium.

Intuitive explanation

The key is to compare the system's current state to equilibrium using the reaction quotient $Q_p$ . Calculate $Q_p$ from the given pressures using the same expression as $K_p$ , then see whether $Q_p$ is smaller or larger than $K_p = 51$ —this tells you which direction the reaction must shift to reach equilibrium and thus whether $HI$ will increase or decrease.

Intuitive explanation

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