One mole of a gas is allowed to expand adiabatically and irreversibly from a volume of 4 litres to a volume of 8 litres against the constant external pressure of one atm. Calculate internal energy change `(Delta U)` of system.

Explanation

To solve the problem of calculating the internal energy change (ΔU) of a gas expanding adiabatically and irreversibly, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Information:**
- Initial volume (V_initial) = 4 L
- Final volume (V_final) = 8 L
- External pressure (P_ext) = 1 atm
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