Exciting Chemistry Problem: Calculate Heat of Reaction!

What is the heat of reaction when 2.50 moles of H2 are reacted with 1.25 moles of O2 to form water vapor?

Choices:

1. 120 kJ/mol
2. 180 kJ/mol
3. 210 kJ/mol
4. 240 kJ/mol

Answer:

240 kJ/mol

In this exciting chemistry problem, we are asked to calculate the heat of reaction when 2.50 moles of H2 react with 1.25 moles of O2 to form water vapor. The reaction can be represented as:

2H2 (g) + O2 (g) -> 2H2O (g)

The balanced equation shows that for every 2 moles of H2 reacted, 2 moles of water vapor are formed. Therefore, if 2.50 moles of H2 react, 2.50 moles of water vapor will be produced.

The heat of reaction can be calculated using the formula:

ΔH = Σ(ΔHf products) - Σ(ΔHf reactants)

Given that the standard enthalpy change of formation of water vapor (ΔHf) is -285.8 kJ/mol and the reaction produces 2 moles of water vapor, we can calculate:

ΔH = 2(ΔHf H2O) - [2(ΔHf H2) + ΔHf O2]

ΔH = 2(-285.8 kJ/mol) - [2(0 kJ/mol) + 0 kJ/mol]

ΔH = -571.6 kJ/mol

Therefore, the heat of reaction when 2.50 moles of H2 react with 1.25 moles of O2 to form water vapor is 240 kJ/mol. Chemistry is truly fascinating!