Khan Academy- ICE Tables in Equilibrium

What ICE Tables Actually Are (And Why Your Chemistry Class Requires Them)

ICE stands for Initial, Change, and Equilibrium. That's it. Three rows. One table. The tool that turns chaotic equilibrium problems into something you can actually solve with numbers instead of guesswork.

If you've been staring at equilibrium problems and feeling lost, ICE tables are your way out. They force you to organize the information the problem gives you, apply the stoichiometry, and then solve for what you actually need.

The Three Rows Explained

Initial: Starting concentrations or partial pressures before the reaction reaches equilibrium. This comes straight from the problem statement.

Change: How much each species changes to reach equilibrium. This is where stoichiometry comes in—you use the coefficients to determine relative changes.

Equilibrium: Initial plus change. These are the values you plug into your equilibrium expression.

Setting Up Your ICE Table: Step by Step

Here's how to actually build one without getting tangled up.

Step 1: Write the Balanced Equation

No exceptions. The coefficients must be correct before you touch the table. If your equation isn't balanced, everything downstream will be wrong.

Example: N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Step 2: Label Your Columns

Each column represents one species in the balanced equation. Include all reactants and products.

Step 3: Fill the Initial Row

Use the concentrations the problem gives you. If a species isn't mentioned initially, assume it's zero. Write "—" or "0" if nothing is there to start.

Step 4: Define the Change Using "x"

This is where students mess up most often. The change row must follow the stoichiometry. If the reaction proceeds by x moles/L, then:

Reactants decrease (they get consumed)
Products increase (they get formed)

For our example: if [N₂] decreases by x, then [H₂] decreases by 3x, and [NH₃] increases by 2x.

Step 5: Write the Equilibrium Expressions

Add the Initial and Change rows to get Equilibrium values. Then plug these into your equilibrium constant expression (K_c or K_p).

Solving ICE Table Problems

Once you've set up the table correctly, you have three paths to the answer:

Method 1: Quadratic Equation

Most equilibrium problems end up here. After substituting equilibrium concentrations into your K expression, you'll have an equation that looks like ax² + bx + c = 0. Solve for x using the quadratic formula.

Know this formula by heart: x = (-b ± √(b² - 4ac)) / 2a

Method 2: The 5% Rule

If K is very small (typically less than 10⁻³), you can often assume x is negligible compared to initial concentrations. This simplifies the math significantly.

Check your answer: if x/[initial] × 100% is less than 5%, your approximation is valid. If not, go back and solve the quadratic.

Method 3: Approximation for Large K

When K is very large, the reaction essentially goes to completion. You can often treat the product formation as if the reactant is fully consumed, then work backward.

Khan Academy's Approach to ICE Tables

Khan Academy covers ICE tables in their Chemical equilibrium unit. Here's what you'll find there and how to use it effectively.

What Khan Academy Gets Right

Clear video walkthroughs with worked examples
Step-by-step problem solving broken into digestible pieces
Practice problems with immediate feedback
Connection between ICE tables and K expressions explained clearly

How to Use Khan Academy for ICE Tables

Don't just watch passively. When you watch their videos, pause before they reveal the next step and try it yourself. The value is in the practice, not the viewing.

Work through their practice problems until you can set up an ICE table without referencing the videos. That's when you've actually learned it.

Common ICE Table Mistakes (And How to Avoid Them)

Mistake	What Goes Wrong	Fix
Wrong stoichiometry in Change row	Everything downstream is wrong	Always use coefficients from balanced equation
Forgetting to account for initial products	Sign error in Change row	Read problem carefully—products aren't always zero initially
Solving for x incorrectly	Wrong equilibrium concentrations	Check your algebra before substituting
Ignoring units	K values don't match expected	Confirm Kc vs Kp—convert if necessary
Not checking the 5% approximation	Significant error in final answer	Always verify x is actually negligible

Getting Started: Your First ICE Table Problem

Try this one:

At 25°C, the equilibrium constant Kc = 4.0 × 10⁻³ for the reaction:

PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)

If you start with 0.10 M PCl₅ and no products, what are the equilibrium concentrations?

Solution

1. Set up the table:

	PCl₅	PCl₃	Cl₂
Initial	0.10	0	0
Change	-x	+x	+x
Equilibrium	0.10 - x	x	x

2. Write the K expression:

Kc = [PCl₃][Cl₂] / [PCl₅] = x² / (0.10 - x) = 4.0 × 10⁻³

3. Solve:

Assuming x is small: x² / 0.10 = 4.0 × 10⁻³

x² = 4.0 × 10⁻⁴

x = 0.020 M

4. Check the approximation:

0.020 / 0.10 × 100% = 20% (this exceeds 5%, so solve the quadratic)

Solving x² + 0.004x - 0.0004 = 0 gives x = 0.017 M

5. Final answer:

[PCl₅] = 0.083 M, [PCl₃] = 0.017 M, [Cl₂] = 0.017 M

The Bottom Line

ICE tables aren't optional busywork. They're the systematic approach that makes equilibrium problems solvable. Khan Academy gives you the practice resources—use them. But don't just watch. Work problems until the process is automatic.

If you're still struggling after working through 10+ problems, your issue isn't ICE tables. It's likely algebra or reading comprehension. Check those foundations first.