ICE tables, which stand for Initial, Change, and Equilibrium, are a systematic way to track the concentrations of reactants and products during a chemical reaction. They are particularly useful in finding equilibrium concentrations and calculating equilibrium constants. Below are three diverse examples that illustrate how to effectively use ICE tables in equilibrium calculations.
This example involves the equilibrium reaction between nitrogen dioxide (NO₂) and dinitrogen tetroxide (N₂O₄), which is a common reaction in atmospheric chemistry.
NO₂ (g) ⇌ N₂O₄ (g)
Change in Concentration: At equilibrium, let x be the amount of NO₂ that reacts. Therefore, the changes in concentration will be:
Equilibrium Concentrations:
ICE Table:
Species | Initial (M) | Change (M) | Equilibrium (M) |
---|---|---|---|
NO₂ | 0.50 | -x | 0.50 - x |
N₂O₄ | 0 | +x | x |
Equilibrium Constant Expression: The equilibrium constant (Kc) for this reaction is given by:
Kc = [N₂O₄] / [NO₂]²
Substituting Equilibrium Concentrations:
Kc = x / (0.50 - x)²
The value of x can be solved if a specific value for Kc is provided. This example illustrates a straightforward application of ICE tables to find equilibrium concentrations.
In this example, we will look at the equilibrium reaction of the formation of ammonia from nitrogen and hydrogen gases:
N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)
Change in Concentration: At equilibrium, let y be the amount of N₂ that reacts, which will affect the concentrations as follows:
Equilibrium Concentrations:
ICE Table:
Species | Initial (M) | Change (M) | Equilibrium (M) |
---|---|---|---|
N₂ | 1.00 | -y | 1.00 - y |
H₂ | 3.00 | -3y | 3.00 - 3y |
NH₃ | 0 | +2y | 2y |
Equilibrium Constant Expression: The equilibrium constant (Kc) is given by:
Kc = [NH₃]² / ([N₂][H₂]³)
Substituting Equilibrium Concentrations:
Kc = (2y)² / ((1.00 - y)(3.00 - 3y)³)
This example highlights how to tackle more complex reactions using ICE tables. The challenge lies in carefully tracking the stoichiometric coefficients during changes in concentration.
This example explores how to use ICE tables to determine the direction of the shift in equilibrium when a change in concentration occurs. The reaction is:
A (g) ⇌ B (g)
Change in Concentration: Suppose we increase the concentration of B to 0.50 M. We want to find out how the equilibrium shifts.
ICE Table Before Change:
Species | Initial (M) | Change (M) | Equilibrium (M) |
---|---|---|---|
A | 0.70 | -x | 0.70 - x |
B | 0.30 | +x | 0.30 + x |
Initial Reaction Quotient (Q):
Q = [B] / [A] = 0.30 / 0.70 = 0.43
Equilibrium Constant (K): Assume K is 0.50. Since Q < K, the reaction will shift to the right to form more B.
New ICE Table After Change:
Species | Initial (M) | Change (M) | Equilibrium (M) |
---|---|---|---|
A | 0.70 | -y | 0.70 - y |
B | 0.50 | +y | 0.50 + y |
This example demonstrates the use of ICE tables not only for calculating equilibrium concentrations but also for predicting the direction of a reaction based on changes in concentration and the comparison of Q and K values.