Chemistry - Thermochemistry Question with Solution | TestHub
Match the columns
Column I | Column II |
|---|---|
P) CO(g) + 1/2O2(g) → CO2(g) | i) Δr H° = Δf H° |
Q) Fe(s) → Fe(g) | ii) Δr H° = Δatomization H° |
R) C(diamond) → C(graphite) | iii) Δr H° = Δtransition H° |
S) C (graphite) + 2H2(g) → CH4(g) | iv) Δr H° = Δc H° |
(Column I = Reaction; Column II = Δr H° equals)
Options:
Answer:
Solution:
P: CO is a compound, so its burning is the combustion of CO, not a formation from elements (P-iv).
Q: Converting solid iron into gaseous Fe atoms is the atomization of iron (Q-ii).
R: Converting one allotropic form (diamond) into another (graphite) is an allotropic transition enthalpy (R-iii).
S: The formation of 1 mol of CH₄ from graphite and H₂ (the standard states of its elements) is the formation of methane and involves no burning (S-i).
The key distinction lies between P and S: combustion requires an element or fuel as a reactant, whereas formation requires elements in their standard states as reactants.
Answer: P-iv; Q-ii; R-iii; S-i.
