Answer is: 125,55 kJ.
Chemical reaction: 2C₂H₂(g) + 5O₂(g) → 4CO₂(g) + 2H₂O(g) ΔH = -2511 kJ.
ΔH = -2511 ÷ 2 = -1255,5 kJ for 1 mol.
m(C₂H₂) = 2,60 g.
n(C₂H₂) = m(C₂H₂) ÷ M(C₂H₂).
n(C₂H₂) = 2,60 g ÷ 26 g/mol = 0,1 mol.
Q = ΔH · n.
Q = 1255,5kJ · 0,1 mol = 125,55 kJ.
