Gibbs Free Energy of Reaction (ΔG rxn) Calculator for 2HNO3
Calculate ΔG rxn
This calculator determines the Gibbs Free Energy for a chemical reaction based on the standard Gibbs free energies of formation (ΔGf°) of the reactants and products. The default values are set for the reaction: N₂O₅(g) + H₂O(l) → 2HNO₃(aq).
Reactants
Standard Gibbs free energy of formation for dinitrogen pentoxide gas.
Standard Gibbs free energy of formation for liquid water.
Products
Standard Gibbs free energy of formation for aqueous nitric acid (approximated as NO₃⁻).
Result
What is Gibbs Free Energy of Reaction (ΔG rxn)?
The Gibbs Free Energy of Reaction, denoted as ΔG rxn, is a thermodynamic quantity that represents the maximum amount of non-expansion work that can be extracted from a closed system at a constant temperature and pressure. It is a crucial indicator of the spontaneity of a chemical reaction. A negative ΔG rxn indicates a spontaneous reaction (exergonic), a positive ΔG rxn indicates a non-spontaneous reaction (endergonic), and a ΔG rxn of zero means the reaction is at equilibrium.
Formula and Explanation
The standard Gibbs Free Energy of Reaction (ΔG°rxn) is calculated using the standard Gibbs free energies of formation (ΔGf°) of the products and reactants:
ΔG°rxn = ΣnΔGf°(products) – ΣmΔGf°(reactants)
Where ‘n’ and ‘m’ are the stoichiometric coefficients of the products and reactants in the balanced chemical equation.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| ΔGf° | Standard Gibbs Free Energy of Formation | kJ/mol | -1000 to 1000 |
| n, m | Stoichiometric Coefficient | Unitless | 1 to 10 |
| ΔG°rxn | Standard Gibbs Free Energy of Reaction | kJ/mol | Varies |
Practical Examples
Example 1: Formation of Nitric Acid
For the reaction N₂O₅(g) + H₂O(l) → 2HNO₃(aq), using the default values in the calculator:
- ΔGf° of N₂O₅(g) = 117.1 kJ/mol
- ΔGf° of H₂O(l) = -237.2 kJ/mol
- ΔGf° of HNO₃(aq) = -111.3 kJ/mol
ΔG°rxn = [2 * (-111.3)] – [1 * (117.1) + 1 * (-237.2)] = -102.5 kJ/mol
Example 2: A Different Reaction
Let’s consider another reaction: 2H₂(g) + O₂(g) → 2H₂O(l)
- ΔGf° of H₂(g) = 0 kJ/mol (element in standard state)
- ΔGf° of O₂(g) = 0 kJ/mol (element in standard state)
- ΔGf° of H₂O(l) = -237.2 kJ/mol
ΔG°rxn = [2 * (-237.2)] – [2 * (0) + 1 * (0)] = -474.4 kJ/mol
How to Use This Gibbs Free Energy Calculator
- Enter Reactant Information: Input the standard Gibbs free energy of formation (ΔGf°) and stoichiometric coefficients for each reactant.
- Enter Product Information: Input the ΔGf° and stoichiometric coefficients for each product.
- Calculate: Click the “Calculate” button to see the Gibbs Free Energy of the reaction.
- Interpret Results: A negative result means the reaction is spontaneous under standard conditions.
Key Factors That Affect Gibbs Free Energy
- Temperature: ΔG is dependent on temperature, as shown in the equation ΔG = ΔH – TΔS.
- Pressure: Changes in pressure can affect the Gibbs free energy, especially for reactions involving gases.
- Concentration: The Gibbs free energy changes as the concentrations of reactants and products change.
- Enthalpy Change (ΔH): The heat absorbed or released during a reaction is a major component of Gibbs free energy.
- Entropy Change (ΔS): The change in the disorder of a system also significantly impacts Gibbs free energy.
- State of Matter: The physical state (solid, liquid, gas) of the reactants and products affects their standard Gibbs free energy values.
Frequently Asked Questions (FAQ)
- What does a negative ΔG rxn mean?
- A negative ΔG rxn indicates that the reaction is spontaneous in the forward direction under standard conditions.
- Can ΔG rxn be positive?
- Yes, a positive ΔG rxn means the reaction is non-spontaneous and requires energy input to proceed.
- What if ΔG rxn is zero?
- If ΔG rxn is zero, the reaction is at equilibrium, and the rates of the forward and reverse reactions are equal.
- How does temperature affect spontaneity?
- For reactions with a positive entropy change (ΔS), increasing the temperature can make a non-spontaneous reaction spontaneous. For reactions with a negative ΔS, increasing the temperature can make a spontaneous reaction non-spontaneous.
- Where can I find standard Gibbs free energy of formation values?
- These values are typically found in chemistry textbooks, handbooks, and online databases like the NIST Chemistry WebBook.
- Is this calculator for any chemical reaction?
- Yes, while it’s pre-filled for the formation of nitric acid, you can input the values for any chemical reaction with one or two reactants and one product.
- What are “standard conditions”?
- Standard conditions are typically defined as 298.15 K (25 °C) and 1 atm pressure for gases, and 1 M concentration for solutions.
- Why is the ΔGf° of elements like H₂ and O₂ zero?
- The standard Gibbs free energy of formation of an element in its most stable form at standard conditions is defined as zero.
Related Tools and Internal Resources
- Enthalpy of Reaction Calculator – Calculate the heat of a reaction.
- Entropy of Reaction Calculator – Determine the change in disorder.
- Chemical Equation Balancer – Balance your chemical equations.
- Thermodynamics Calculator – A suite of tools for thermodynamics.
- In-depth Article on Gibbs Free Energy
- Introduction to Chemical Kinetics