Chemical Equilibrium

ICE Table

Determine Equilibrium Constant Using ICE Table Method

In this video let's go through how to determine equilibrium constant Kc using the ICE table method.

Given this simple example:

2.00 moles of $SO_2$ and 2.00 moles of $O_2$ are mixed and allowed to reach equilibrium in a 0.50 $dm^3$ container via reaction:
 $2SO_2$ (g) +  $O_2$ (g) ⇌ $2SO_3$ (g)

If conversion of  $SO_2$  is 20%, determine Kc

2SO₂(g) + O₂(g) ⇌ 2SO₃(g)

• First we have to write out the balanced equation and 3 additional rows which represents the following:

• I - INITIAL number of moles

  C - CHANGE in number of moles

  E - EQUILIBRIUM number of moles

• The initial moles of SO₂ and O₂ are both given as 2.00 moles, so we call put that info into the ICE table.

• Also the conversion of SO₂ is 20% which works out to be 0.4 moles of SO₂ reacted, and we can put that in as well.

Given this equation:

H₂ + I₂ ⇌ 2HI

Calculate all three equilibrium concentrations when

[H₂]_o = [I₂]_o = 0.200 M and K_c = 64.0.

H₂ + I₂ ⇌ 2HI

• Now, let's fill in the initial row. This should be pretty easy:

• The first two values were specified in the problem and the last value ([HI] = 0) come from the fact that the reaction has not yet started, so no HI could have been produced yet.

Now for the change row. 

• The minus sign comes from the fact that the H₂ and I₂ amounts are going to go down as the reaction proceeds.

• x signifies that we know some H₂ and I₂ get used up, but we don't know how much. What we do know is that an EQUAL amount of each will be used up. We know this from the coefficients of the equation.

• For every one H₂ used up, one I₂ is used up also.

 $H_{2_{ }}$  +  $I_2$   ⇌  $2HI$  

 $Kc\ =\ \frac{\left[HI\right]^2}{\left[H_2\right]\left[I_2\right]}$  
 $64\ =\ \frac{\left(2x\right)^2}{\left(0.2\ -\ x\right)\left(0.2\ -\ x\right)}$  
 $x=\ 0.16\ mol\ dm^{-3}$  

Multiple Choice

Nitrogen and oxygen do not react appreciably at room temperature, as illustrated by our atmosphere. But at high temperatures, the reaction below can proceed to a measurable extent.

N₂(g) + O₂(g) ⇌ 2NO(g)

At 3000 K, the reaction above has K_c = 0.0153. If 0.3000 mol of pure NO is injected into an evacuated 2.000 L container and heated to 3000 K, what will be the equilibrium concentration of NO?

• 0.0096 mol dm^-3

• 0.0706 mol dm^-3

Multiple Choice

At a particular temperature, K_c = 2.0 x 10¯⁶ for the reaction:

2CO₂(g) ⇌ 2CO(g) + O₂(g)

If 2.0 mol CO₂ is initially placed into a 5.0 L vessel, calculate x?

• x = 4.3 x 10¯³ M

• x = 4.3 x 10^-2 M

Poll

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