Chemistry - Thermochemistry Question with Solution | TestHub
Match the following
Column I | Column II |
|---|---|
P) H2(g) + Cl2(g) → 2HCl(g) | i) ΔH = ΔU + RT |
Q) 2NO(g) + O2(g) → 2NO2(g) | ii) ΔH = ΔU |
R) H2(g) + I2(s) → 2HI(g) | iii) ΔH = ΔU - 2RT |
S) N2(g) + 3H2(g) → 2NH3(g) | iv) ΔH = ΔU - RT |
(Column I = Reaction; Column II = Relation)
Options:
Answer:
Solution:
To determine the relationship between enthalpy change (Δ H) and internal energy change (Δ U), we use the equation:
Δ H = Δ U + Δ ngRT
where Δ ng represents the change in the number of moles of gaseous products minus the moles of gaseous reactants.
For each reaction:
P: Δ ng = 2 - 2 = 0. Therefore, Δ H = Δ U. This corresponds to option (ii).
Q: Δ ng = 2 - 3 = -1. Therefore, Δ H = Δ U - RT. This corresponds to option (iv).
R: In this reaction, I₂ is a solid. Thus, we only consider the gaseous moles. Δ ng = 2 - 1 = +1. Therefore, Δ H = Δ U + RT. This corresponds to option (i).
S: Δ ng = 2 - 4 = -2. Therefore, Δ H = Δ U - 2RT. This corresponds to option (iii).
The correct matching is: P-ii; Q-iv; R-i; S-iii.
