# Answer the following question. Calculate ΔU at 298 K for the reaction, C2H4(g) + HCl(g) → C2H5Cl(g), ΔH = - 72.3 kJ How much PV work is done? - Chemistry

Sum

Calculate ΔU at 298 K for the reaction,

C2H4(g) + HCl(g) → C2H5Cl(g), ΔH = - 72.3 kJ

How much PV work is done?

#### Solution

Given:
Enthalpy change = ΔH = –72.3 kJ
Temperature = T = 298 K

To find:
PV work done and internal energy change (ΔU)

Formulae:
1. W = - ΔngRT

2. ΔH = ΔU + ΔngRT

Calculations:

Δng = (moles of product gases) - (moles of reactant gases)

Δng = 1 – 2 = –1 mol

Using formula (i)

W = - ΔngRT

= - (- 1 mol) × 8.314 J K-1 mol-1 × 298 K

= 2477.57 J = 2.48 kJ

Now, using formula (ii) and rearranging,

ΔU = ΔH - Δ ngRT = ΔH + W = –72.3 kJ + 2.48 kJ = –69.8 kJ

∴ The PV work done is 2.48 kJ.

∴ The internal energy change (ΔU) is –69.8 kJ.

Concept: Enthalpy (H)
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#### APPEARS IN

Balbharati Chemistry 12th Standard HSC for Maharashtra State Board
Chapter 4 Chemical Thermodynamics
Exercise | Q 4.12 | Page 88