Given H2 + F2 → 2HF ∆H= -537 kJ How much heat is required to react 3 g F2 with H2?

Question

Thermochemical equations

Answer 1

H2 + F2 ==> 2HF ∆H = -537 kJ

3 g F2 x 1 mol F2/38 g = 0.0789 moles

1 mol F2 reacts with 1 mol H2 and generates 537 kJ of heat

0.0789 moles F2 x 537 kJ/mol F2 = 42.4 kJ = 40 kJ of heat generated (to 1 sig. fig.)

Note: The question asks how much heat is required but since the sign of ∆H is negative, this indicates heat is evolved or generated, not needed.