1. What is Standard Enthalpy of Reaction at Equilibrium?

Definition: This calculator determines the change in enthalpy (ΔH) for a chemical reaction at equilibrium based on temperature, entropy change, and equilibrium constant.

Purpose: It helps chemists and chemical engineers understand the energy changes in chemical reactions at equilibrium conditions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \Delta H \) — Change in enthalpy (J/kg)
• \( T \) — Temperature (K)
• \( \Delta S \) — Change in entropy (J/kg·K)
• \( [R] \) — Universal gas constant (8.314 J/mol·K)
• \( K_c \) — Equilibrium constant (mol/m³)

Explanation: The formula relates the thermodynamic quantities at equilibrium, accounting for both entropy changes and the equilibrium constant.

3. Importance of Enthalpy Calculation

Details: Knowing ΔH helps predict whether a reaction is exothermic (releases heat) or endothermic (absorbs heat), which is crucial for process design and safety.

4. Using the Calculator

Tips: Enter the temperature in Kelvin, entropy change in J/kg·K, and equilibrium constant in mol/m³. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is the significance of the equilibrium constant?
A: The equilibrium constant (K_c) indicates the ratio of product concentrations to reactant concentrations at equilibrium.

Q2: Why do we use log₁₀ in the formula?
A: The logarithmic relationship comes from the connection between Gibbs free energy and the equilibrium constant.

Q3: What are typical units for these calculations?
A: Standard units are Kelvin for temperature, J/kg·K for entropy, and mol/m³ for equilibrium constant.

Q4: Can this be used for any chemical reaction?
A: Yes, as long as you have the necessary thermodynamic data and the reaction is at equilibrium.

Q5: How does temperature affect the result?
A: Temperature appears twice in the formula, so its effect depends on the relative magnitudes of the entropy term and the equilibrium constant term.