ICE Table Practice: Equilibrium Calculations

Fill in the missing initial, change, and equilibrium entries, then use your table to answer the equilibrium-constant questions. Symbolic answers like 0.200 - x and +2x are accepted with any spacing.

New to the method? Read the ICE tables lesson first.

1. Simple 1:1 dissociation

Intro

H₂(g) + I₂(g) ⇌ 2 HI(g)

A sealed flask is charged with 0.200 M H₂ and 0.200 M I₂. No HI is present initially. Let x be the molarity of H₂ that reacts.

ICE table for H2(g) + I2(g) <-> 2 HI(g). Enter the missing values.
	H₂	I₂
Initial (M)	0.200	0.200
Change (M)	-x
Equilibrium (M)

Equilibrium questions

At equilibrium [HI] = 0.320 M. What is x (in M)?

Using x, calculate K_c for the reaction.

2. Testing the small-x approximation

Core

N₂O₄(g) ⇌ 2 NO₂(g)

0.100 M N₂O₄ is placed in an empty flask at 298 K, where K_c = 4.6 × 10⁻³. Let x be the molarity of N₂O₄ that dissociates. Use the approximation only to estimate x first; then test whether that estimate is valid.

ICE table for N2O4(g) <-> 2 NO2(g). Enter the missing values.
	N₂O₄	NO₂
Initial (M)	0.100
Change (M)
Equilibrium (M)

Equilibrium questions

First estimate x (in M) by using 0.100 - x ≈ 0.100 in K_c = 4x² / (0.100 - x).

Using your estimated x, calculate x / 0.100 × 100. Enter the percentage (not the decimal). Does it meet the 5% criterion?

Because the 5% check fails, solve the exact expression 4x² / (0.100 - x) = 4.6 × 10⁻³ for the physically meaningful value of x (in M).

Using the exact value of x, what is [NO₂] at equilibrium (in M)?

3. Weak acid ionization

Core

CH₃COOH(aq) ⇌ H⁺(aq) + CH₃COO⁻(aq)

0.250 M acetic acid ionizes in water. K_a = 1.8 × 10⁻⁵. Ignore the small amount of H⁺ from water. Let x be the molarity of acid that ionizes.

ICE table for CH3COOH(aq) <-> H+(aq) + CH3COO-(aq). Enter the missing values.
	CH₃COOH	H⁺
Initial (M)	0.250
Change (M)
Equilibrium (M)		x

Equilibrium questions

Solve for [H⁺] at equilibrium (in M), using the small-x approximation.

What is the pH of the solution?

4. Reaction started with products

Challenge

PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)

A flask initially contains 0.400 M PCl₅ and 0.100 M Cl₂, with no PCl₃. Let x be the molarity of PCl₅ that decomposes.

ICE table for PCl5(g) <-> PCl3(g) + Cl2(g). Enter the missing values.
	PCl₅	Cl₂
Initial (M)	0.400	0.100
Change (M)
Equilibrium (M)

Equilibrium questions

If x = 0.150 M at equilibrium, what is [Cl₂] (in M)?

Calculate K_c using x = 0.150 M.

5. Quadratic required

Challenge

CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)

0.500 M CO and 0.500 M H₂O react at a temperature where K_c = 4.00. Let x be the molarity of CO that reacts.

ICE table for CO(g) + H2O(g) <-> CO2(g) + H2(g). Enter the missing values.
	CO	H₂O
Initial (M)	0.500	0.500
Change (M)	-x
Equilibrium (M)

Equilibrium questions

Solve x² / (0.500 - x)² = 4.00 for x (in M). Take the square root of both sides first.

What is [CO] at equilibrium (in M)?

1. Simple 1:1 dissociation

Equilibrium questions

2. Testing the small-x approximation

Equilibrium questions

3. Weak acid ionization

Equilibrium questions

4. Reaction started with products

Equilibrium questions

5. Quadratic required

Equilibrium questions

Reference sheetPeriodic table and AP equations in a resizable window