t Calculating Equilibrium Constants The equilibrium constant, K, of a reaction a

Question

t Calculating Equilibrium Constants The equilibrium constant, K, of a reaction at a particular temperature is determined by the concentrations or pressures of the reactants and products at equilibrium. For a gaseous reaction with the general form aA bB cC dD the KC and K. expressions are given by p Cl D A B (FC) (PD) PA) (PB) The subscript c or p indicates whether K is expressed in terms of concentrations or pressures. Equilibrium-constant expressions do not include a term for any pure solids or liquids that may be involved since their composition does not change throughout the reaction. The standard state of a pure substance is the pure substance itself, and although the quantity may change the sample remain pure. The concentration is effectively equal to 1, and will not impact the magnitude of K 0.169 Submit Hints My Answers Give Up Review Part Correct Deriving concentrations from data In Part A, you were given the equilibrium pressures, which could be plugged directly into the formula for K. In Part B however, you will be given initial concentrations and only one equilibrium concentration. You must use this data to find a three equilibrium concentrations before you can apply the formula for K Part B The following reaction was performed in a sealed vessel at 768 C Initially, only H2 and I2 were present at concentrations of H2 3.55M and I 2.40M. The equilibrium concentration of I is 0.0300 M. What is the equilibrium constant, Kc,for the reaction at this temperature? Express your answer numerically.

Explanation / Answer

To do this, you only need to write the overall reaction and then use an ICE chart:

reaction: H2(g) + I2(g) <---------> 2HI(g)

innitial: 3.55 2.40 0

equilibrium: 3.55-x 0.03 2x

Now, we know that I2 in equilibrium is 0.03, so the difference of this value with the innitial data, will give us the quantities that H2 is losing, which will be the same quantity of the product formed so:

[I2]eq = [I2]i - x

x = [I2]eq - [I2]i

EDITED TO CORRECT THE VALUE OF I2

x = 2.40 - 0.03 = 2.37 M

Now the value of H2 would be:

[H2]eq = 3.55 - 2.37 = 1.18 M

[HI]eq = 2*2.37 = 4.74 M

With this, Kc may be calculated:

Kc = (4.74)2 / (0.03)*(1.18)

Kc = 634.68

Hope this helps

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