Question

For the reaction H2(g) + I2(g) 2HI(g), Kc = 50.2 at 445ºC. If [H2] = [I2] = [HI] = 1.75  10-3 M at 445ºC, which one of these statements is true? A) The system is at equilibrium, thus no concentration changes will occur. B) The concentrations of HI and I2 will increase as the system approaches equilibrium. C) The concentration of HI will increase as the system approaches equilibrium. D) The concentrations of H2 and HI will fall as the system moves toward equilibrium. E) The concentrations of H2 and I2 will increase as the system approaches equilibrium

Answer 1

Answer: C) The concentration of HI will increase as the system approaches equilibrium.

Explanation:

Equilibrium constant is defined as the ratio of concentration of products to the concentration of reactants each raised to the power their stoichiometric ratios. It is expressed as $K_c$

K is the constant of a certain reaction when it is in equilibrium, while Q is the quotient of activities of products and reactants at any stage other than equilibrium of a reaction.

For the given chemical reaction:

$H_2(g)+I_2(g)\rightarrow 2HI(g)$

The expression for $Q_c$ is written as:

$Q_c=\frac{[HI]^2}{[H_2]^1[I_2]^1}$

$Q_c=\frac{(1.75\times 10^{-3})^2}{(1.75\times 10^{-3})^1\times (1.75\times 10^{-3})^1}$

$Q_c=1.00$

$K_c=50.2$

Thus as $K_{eq}>Q$ , the reaction will shift towards the right i.e. towards the product side.