Chemistry - Thermochemistry Question with Solution | TestHub
Carefully observe the given diagram which indicates standard enthalpy of formation of different states of one mole of Ca and two moles of Cl atoms and match the entries in Column I and II provided.
Column I | Column II |
|---|---|
P) Δf H [Ca2+(aq)] | i) -100 kJ/mol |
Q) Δf H [Cl-(aq)] | ii) -2000 kJ/mol |
R) ΔHHydration [Ca2+(g)] | iii) -400 kJ/mol |
S) Lattice enthalpy of CaCl2(s) | iv) +2200 kJ/mol |
(Column I = Quantity; Column II = Value)
Options:
Answer:
Solution:
Read level differences from the diagram. S: lattice enthalpy = [Ca2+(g) + 2Cl-(g)] - [CaCl2(s)] = 1500 - (-700) = +2200 kJ/mol, S-iv. Q: from [Ca2+(g) + Cl2(g)] to [Ca2+(g) + 2Cl-(aq)], ΔH = 1100 - 1900 = -800 kJ for 2 mol Cl-(aq), so Δf H[Cl-(aq)] = -400 kJ/mol, Q-iii. R: hydration of Ca2+ = [Ca2+(aq) + 2Cl-(aq)] - [Ca2+(g) + 2Cl-(aq)] = -900 - 1100 = -2000 kJ/mol, R-ii. P: Δf H[Ca2+(aq)] = -900 - 2(-400) = -100 kJ/mol, P-i. Ans: P-i; Q-iii; R-ii; S-iv.
