1. What is the Reaction Quotient for Water?

The reaction quotient (Q) for water describes the ratio of product concentrations to reactant concentrations at any point during the water autoionization reaction. It helps determine whether the system is at equilibrium or which direction the reaction will proceed to reach equilibrium.

2. How Does the Calculator Work?

The calculator uses the reaction quotient equation:

Where:

• \( [H^+] \) — Hydrogen ion concentration (M)
• \( [OH^-] \) — Hydroxide ion concentration (M)
• \( [H_2O] \) — Water concentration (M)

Explanation: The equation calculates the instantaneous ratio of product concentrations to reactant concentration for the water autoionization reaction.

3. Importance of Q Calculation

Details: Comparing Q to the equilibrium constant (Kw) indicates whether the system is at equilibrium (Q = Kw), will produce more products (Q < Kw), or will produce more reactants (Q > Kw).

4. Using the Calculator

Tips: Enter all concentrations in molarity (M). For pure water at 25°C, [H+] = [OH-] = 1×10⁻⁷ M and [H2O] ≈ 55.5 M.

5. Frequently Asked Questions (FAQ)

Q1: What is the equilibrium constant (Kw) for water?
A: At 25°C, Kw = 1.0×10⁻¹⁴ M². This is the special case of Q when the system is at equilibrium.

Q2: How does temperature affect Q and Kw?
A: Both Q and Kw are temperature dependent. Kw increases with temperature as the autoionization of water is endothermic.

Q3: Why is water concentration included in Q but not Kw?
A: In Kw, water concentration is essentially constant and incorporated into the equilibrium constant value. In Q calculations for non-equilibrium states, explicit water concentration is needed.

Q4: What does it mean if Q < Kw?
A: The system will proceed in the forward direction (more H+ and OH- will form) to reach equilibrium.

Q5: How is this different from pH calculations?
A: pH focuses specifically on [H+], while Q considers the complete reaction quotient including all species in the water autoionization reaction.