Clarifying the [C] Portion of ICE Tables: A Guide for Different Reaction Types and Equilibrium Expressions

Clarifying the [C] Portion of ICE Tables

The [C] section in an ICE table corresponds to the changes in molarity from the balanced chemical equation, accounting for how many moles react or form. This part tracks concentration changes during the reaction.

How to Use [C] for Different Reaction Types

• Reaction goes to completion: Use the initial molarity and adjust across the table. Subtract from reactants, add to products.
• Multiply each change by the stoichiometric coefficient from the balanced equation. For example, if 2 moles of a substance react, multiply the molarity change by 2.
• Reaction at equilibrium: Introduce a variable, typically x, representing molarity change.
• Subtract x times the coefficient on reactants, add it on products. For example, for 2 moles of a product, use +2x in the table.

Strong vs Weak Acids/Bases in ICE Tables

• Strong acids/bases (e.g., HCl, NaOH): Dissociate completely. Their initial molarity values are used directly in [C] without variables.
• Weak acids/bases (e.g., CH3COOH, NH3): Partially dissociate. Use variables like x to represent the change in concentration.

Setting Up Equilibrium Expressions Correctly

When creating the equilibrium expression, include only aqueous and gaseous species. Exclude solids and pure liquids like H2O.

Note that H3O+ and H+ represent the same ion in pH calculations. Both appear equivalently in equilibrium expressions.

Summary of Key Points

• The [C] row shows molarity changes scaled by stoichiometric coefficients from the balanced equation.
• Use variables like x only for reactions not going to completion.
• Strong acids/bases dissociate fully; weak acids/bases partially, affecting how [C] is set.
• Only include relevant aqueous/gaseous species in equilibrium expressions.
• Ignore pure liquids like H2O and treat H3O+ and H+ as equivalent in calculations.

What does the [C] row represent in an ICE table?

The [C] row shows the change in molarity based on the balanced equation. It reflects how much the concentration goes up or down as the reaction proceeds.

How do I handle the coefficients from the balanced equation in the ICE table?

Multiply the molarity change by the number of moles from the balanced equation. For example, if there are 2 moles, use ±2x to show change in concentration.

How do I treat strong acids or bases in an ICE table?

Strong acids and bases dissociate completely. Use their initial molarity values directly in the [C] row, instead of variables like x.

When should I use variables like x in the ICE table?

Use x for weak acids or bases that partially dissociate. The change in molarity is unknown, so you represent it using variables in the [C] row.

Can I include water or solids in the ICE table and equilibrium expression?

No, exclude pure solids and liquids like water from equilibrium expressions. Only aqueous and gaseous species are included.

How do I relate H₃O⁺ and H⁺ when calculating pH?

Treat H₃O⁺ and H⁺ ions as equivalent when calculating pH. They both represent the concentration of hydrogen ions in solution.