Calculate Delta G Rxn Using The Following Information 4hno3 5n2h4

This calculator helps you determine the Gibbs free energy change (ΔG) for the reaction 4HNO₃ + 5N₂H₄ → 4N₂ + 4NH₃ + 10H₂O using standard thermodynamic data. The calculation is based on the standard Gibbs free energies of formation for each compound.

Introduction

The Gibbs free energy change (ΔG) is a fundamental thermodynamic property that indicates the spontaneity of a chemical reaction. A negative ΔG value indicates that the reaction is spontaneous under standard conditions, while a positive ΔG value indicates that the reaction is non-spontaneous.

For the reaction 4HNO₃ + 5N₂H₄ → 4N₂ + 4NH₃ + 10H₂O, we can calculate ΔG using the standard Gibbs free energies of formation (ΔG°f) for each compound involved in the reaction.

Gibbs Free Energy Formula

The standard Gibbs free energy change for a reaction (ΔG°rxn) can be calculated using the following formula:

ΔG°rxn = ΣΔG°f(products) - ΣΔG°f(reactants)

Where:

ΔG°f(products) is the sum of the standard Gibbs free energies of formation for all products
ΔG°f(reactants) is the sum of the standard Gibbs free energies of formation for all reactants

All values should be in the same units (typically kJ/mol).

Calculation Steps

Identify all reactants and products in the balanced chemical equation
Look up the standard Gibbs free energies of formation (ΔG°f) for each compound
Multiply each ΔG°f value by the stoichiometric coefficient from the balanced equation
Sum the ΔG°f values for all products and subtract the sum of the ΔG°f values for all reactants

Note: Standard Gibbs free energies of formation are typically reported at 25°C and 1 atm pressure.

Worked Example

Let's calculate ΔG°rxn for the reaction 4HNO₃ + 5N₂H₄ → 4N₂ + 4NH₃ + 10H₂O using the following standard Gibbs free energies of formation (in kJ/mol):

Compound	ΔG°f (kJ/mol)
HNO₃	-173.9
N₂H₄	-10.8
N₂	0
NH₃	-45.9
H₂O	-237.2

Calculation:

ΔG°rxn = [4(0) + 4(-45.9) + 10(-237.2)] - [4(-173.9) + 5(-10.8)]

= [0 - 183.6 - 2372] - [-695.6 - 54]

= -2555.6 - (-749.6)

= -2555.6 + 749.6

= -1806 kJ/mol

The negative value indicates that the reaction is spontaneous under standard conditions.

Interpreting Results

The calculated ΔG°rxn value provides several important insights:

Spontaneity: A negative ΔG°rxn indicates the reaction is spontaneous under standard conditions
Energy Change: The magnitude of ΔG°rxn indicates the amount of energy released or absorbed
Equilibrium: The value helps predict the position of equilibrium in the reaction

Remember that ΔG°rxn is calculated under standard conditions (25°C, 1 atm). Actual conditions may affect the spontaneity of the reaction.

FAQ

What is the standard Gibbs free energy of formation?

The standard Gibbs free energy of formation (ΔG°f) is the change in Gibbs free energy that accompanies the formation of 1 mole of a compound from its constituent elements in their standard states at 25°C and 1 atm pressure.

How do I find standard Gibbs free energies of formation?

Standard Gibbs free energies of formation can be found in thermodynamic databases, chemistry handbooks, or online resources like the NIST Chemistry WebBook.

What units should I use for ΔG°f values?

It's best to use consistent units throughout your calculations. Typically, kJ/mol is used for standard Gibbs free energies of formation.