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Calculate Delta H for Each of The Following Reactions H2s

Reviewed by Calculator Editorial Team

This calculator helps you determine the enthalpy change (ΔH) for hydrogen sulfide (H2S) reactions using standard thermodynamic data. The enthalpy change is a measure of the heat absorbed or released in a chemical reaction at constant pressure.

Introduction

The enthalpy change (ΔH) for a reaction is calculated using the standard enthalpies of formation (ΔHf) of the products and reactants. The formula for calculating ΔH is:

ΔH = ΣΔHf(products) - ΣΔHf(reactants)

This formula accounts for the energy changes involved in breaking bonds in the reactants and forming bonds in the products. The standard enthalpies of formation are values that represent the change in enthalpy when one mole of a compound is formed from its elements in their standard states.

Formula

The enthalpy change for a reaction is calculated using the following formula:

ΔH = ΣΔHf(products) - ΣΔHf(reactants)

Where:

  • ΔHf(products) is the sum of the standard enthalpies of formation of all products
  • ΔHf(reactants) is the sum of the standard enthalpies of formation of all reactants

This formula is derived from the first law of thermodynamics and Hess's law, which states that the enthalpy change for a reaction is the same regardless of the pathway taken.

Calculation

To calculate the enthalpy change for a reaction involving H2S, follow these steps:

  1. Identify the balanced chemical equation for the reaction
  2. Look up the standard enthalpies of formation for each reactant and product
  3. Multiply each ΔHf value by the stoichiometric coefficient in the balanced equation
  4. Sum the ΔHf values for the products and subtract the sum of the ΔHf values for the reactants

The result will be the enthalpy change for the reaction in kilojoules per mole (kJ/mol). A positive ΔH indicates an endothermic reaction, while a negative ΔH indicates an exothermic reaction.

Example

Let's calculate the enthalpy change for the following reaction:

H2S(g) + 3/2 O2(g) → SO2(g) + H2O(l)

Using standard enthalpies of formation:

  • ΔHf(H2S) = -20.1 kJ/mol
  • ΔHf(O2) = 0 kJ/mol (element in standard state)
  • ΔHf(SO2) = -296.8 kJ/mol
  • ΔHf(H2O) = -285.8 kJ/mol

Applying the formula:

ΔH = [1 × (-296.8) + 1 × (-285.8)] - [1 × (-20.1) + 1.5 × 0] = -582.6 + 20.1 = -562.5 kJ/mol

This result indicates that the reaction is exothermic, releasing 562.5 kJ of energy per mole of H2S reacted.

FAQ

What is the standard enthalpy of formation for H2S?
The standard enthalpy of formation for H2S(g) is -20.1 kJ/mol. This value represents the energy change when one mole of H2S is formed from its elements in their standard states.
How do I balance a chemical equation for ΔH calculation?
To balance a chemical equation, ensure that the number of atoms of each element is the same on both sides of the equation. This ensures that the stoichiometric coefficients can be used in the ΔH calculation.
What is the difference between ΔH and ΔU?
ΔH (enthalpy change) is the heat absorbed or released at constant pressure, while ΔU (internal energy change) is the heat absorbed or released at constant volume. For many chemical reactions, ΔH is more commonly used.