Calculate The Energy Change of The Following Reaction H2+ Br

This calculator determines the energy change (ΔH) for the reaction H₂ + Br₂ → 2HBr using standard enthalpies of formation. The calculation follows Hess's Law of Constant Heat Summation.

How to Calculate the Energy Change

The energy change of a reaction can be calculated using standard enthalpies of formation (ΔHf°). The process involves:

Identify the standard enthalpies of formation for all reactants and products
Calculate the total enthalpy of the reactants
Calculate the total enthalpy of the products
Find the difference between products and reactants to get ΔH

For the reaction H₂ + Br₂ → 2HBr, you'll need the standard enthalpies of formation for H₂(g), Br₂(l), and HBr(g).

Formula Used

The energy change (ΔH) of a reaction is calculated using:

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

Where ΔHf° represents the standard enthalpy of formation for each compound.

For the specific reaction H₂ + Br₂ → 2HBr, the formula becomes:

ΔH = [2 × ΔHf°(HBr)] - [ΔHf°(H₂) + ΔHf°(Br₂)]

Worked Example

Let's calculate the energy change for the reaction using these standard enthalpies of formation:

ΔHf°(H₂) = 0 kJ/mol
ΔHf°(Br₂) = 30.9 kJ/mol
ΔHf°(HBr) = -36.4 kJ/mol

Applying the formula:

ΔH = [2 × (-36.4)] - [0 + 30.9]

ΔH = -72.8 - 30.9

ΔH = -103.7 kJ/mol

This means the reaction releases 103.7 kJ of energy per mole of H₂ that reacts.

Interpreting Results

A negative ΔH indicates an exothermic reaction (energy is released). A positive ΔH indicates an endothermic reaction (energy is absorbed).

In this case, the negative value shows that the formation of HBr from H₂ and Br₂ is an exothermic process.

Note: Actual values may vary slightly depending on the specific conditions and sources of standard enthalpies used.

Frequently Asked Questions

What is the difference between ΔH and ΔE?

ΔH (enthalpy change) refers to heat transfer at constant pressure, while ΔE (internal energy change) refers to heat transfer at constant volume. For most chemical reactions, we use ΔH.

Why are standard enthalpies of formation important?

They provide a consistent reference point for calculating energy changes in chemical reactions, allowing chemists to predict reaction behavior.

Can I use this calculator for other reactions?

Yes, the same principles apply to any chemical reaction where you know the standard enthalpies of formation for all reactants and products.