Question

how much heat is liberated by the combustion of 206 grams of hydrogen?
ΔHcomb= -286kj/mol

Answer 1

2H2 + O2 ==> 2H2O
286 kJ/mol x (1 mol H2/2 g H2) = 143 kJ/gram hydrogen.
So 206 g Hydrogen x (143 kJ/g) = ?? kJ.
Check my thinking.

Answer 2

A sample of ammonia liberates 5.66 kJ of heat as it solidifies at its melting point