Calculate The H of The Following Reaction C2h4 H2 C2h6

This calculator helps you determine the enthalpy change (ΔH) for the reaction C2H4 + H2 → C2H6 using standard enthalpy values and Hess's Law. The reaction involves the hydrogenation of ethylene to form ethane, a common industrial process.

How to Calculate ΔH for This Reaction

The enthalpy change (ΔH) for a reaction can be calculated using standard enthalpies of formation (ΔHf°) for the reactants and products. The process involves:

Finding the standard enthalpies of formation for all reactants and products
Calculating the total enthalpy of the products
Calculating the total enthalpy of the reactants
Determining the enthalpy change by subtracting the total reactant enthalpy from the total product enthalpy

For the reaction C2H4 + H2 → C2H6, we use the following standard enthalpies of formation:

ΔHf° for C2H4 (ethylene) = -78.2 kJ/mol
ΔHf° for H2 (hydrogen gas) = 0 kJ/mol (by definition)
ΔHf° for C2H6 (ethane) = -84.7 kJ/mol

Formula Used

Enthalpy Change Calculation

The enthalpy change (ΔH) for the reaction is calculated using the formula:

ΔH = ΣΔHf°(products) - ΣΔHf°(reactants)

For the specific reaction C2H4 + H2 → C2H6:

ΔH = [ΔHf°(C2H6)] - [ΔHf°(C2H4) + ΔHf°(H2)]

Worked Example

Let's calculate the enthalpy change for the reaction C2H4 + H2 → C2H6 using the standard enthalpies of formation:

Total enthalpy of products: ΔHf°(C2H6) = -84.7 kJ/mol
Total enthalpy of reactants: ΔHf°(C2H4) + ΔHf°(H2) = -78.2 kJ/mol + 0 kJ/mol = -78.2 kJ/mol
ΔH = -84.7 kJ/mol - (-78.2 kJ/mol) = -6.5 kJ/mol

The calculation shows that the reaction releases 6.5 kJ of energy per mole of ethane produced.

Interpreting the Results

The negative ΔH value indicates that the reaction is exothermic, meaning it releases heat to the surroundings. This is typical for hydrogenation reactions where energy is released as new bonds form.

The magnitude of ΔH (6.5 kJ/mol) shows that this reaction is relatively energy-efficient compared to other chemical processes. The small energy release suggests that the reaction is favorable but not extremely exothermic.

Frequently Asked Questions

What is the standard enthalpy of formation?: The standard enthalpy of formation (ΔHf°) is the change in enthalpy that occurs when one mole of a compound is formed from its constituent elements in their standard states.
Why is ΔHf° for H2 defined as 0?: By definition, the standard enthalpy of formation for hydrogen gas (H2) is 0 because it's the most stable form of hydrogen at standard conditions.
How does temperature affect ΔH calculations?: Standard enthalpies of formation are measured at 25°C (298 K). For reactions at different temperatures, you would need to account for temperature effects using heat capacity data.
What units are used for ΔH values?: Standard enthalpy changes are typically reported in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).
How accurate are these calculations?: These calculations use standard thermodynamic data which are generally accurate to within a few percent. For precise industrial applications, experimental measurements may be needed.