Determine the mass (in grams)

Question

Given the balanced chemical equation,

2 H(g) → H₂(g)        ΔH⁰_rxn = −436 kJ/mol

Determine the mass (in grams) of H₂(g) produced when 823 kJ of heat is released.

Answer 1

2 H(g) → H₂(g)        ΔH⁰_rxn = −436 kJ/mol

This tells us that when 2 H combine to form H₂(g), 436 kJ/mol are released.

823 kJ x 1 mol H₂/436 kJ = 1.8876 moles H₂

1.8876 moles H₂ x 2.00 g/mol = 3.775 g = 3.78 g of H₂ (3 sig. figs.)