Given the balanced chemical equation, SiO2 (s) + 4 HF (g) → SiF4 (g) + 2 H2O (l) ΔH°rxn = - 184 kJ Determine the mass (in grams) of HF (g) must react when 345 kJ of energy is released.

mass HF = 150.05 g

Explanation:

SiO2 (s) + 4HF (g) → SiF4 (g) + 2H2O (l)

⇒ Q = (ΔH°rxn * mHF) / (mol HF * MwHF)

∴ MwHF = 20.0063 g/mol

∴ mol HF = 4 mol

∴ ΔH°rxn = - 184 KJ

∴ Q = 345 KJ

mass HF (mHF):

⇒ mHF = (Q * mol HF * MwHF) / ΔH°rxn

⇒ mHF = (345 KJ * 4mol HF * 20.0063 g/mol) / 184 KJ

⇒ mHF = 150.05 g HF