Chemistry - Thermochemistry Question with Solution | TestHub
Enthalpy of combustion of a given compounds is defined as following. It is the change in enthalpy when 1 mole of this compound combines with required amount of O2 to give product in their stable forms. The enthalpy of combustion is usually measured by placing a known mass of the compound in a closed steel container ( known as bomb-calorimeter)
Identify the incorrect statement -
Options:
Answer:
Solution:
(A) ΔH°comb(C, graphite) = ΔH°f(CO₂, g) is true, because combustion of C to CO₂ is same as formation of CO₂.
(B) ΔH°f(H₂O, l) from H₂(g) is true, since it defines formation from elements in standard state.
(C) “Standard enthalpy of combustion is always negative” is true, because combustion is always exothermic (releases heat).
(D) “Standard enthalpy of formation is always negative” is false, because ΔH°f can be positive (e.g., NO(g), O₃(g)).
Hence correct answer: (D).