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Two blocks of the same metal having same mass and at temperature T 1 and T 2 , respectively, are brought in contact with each other and allowed to attain thermal equilibrium at constant pressure. The change in entropy, Δ S, for this process is :

1. 2C p In ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎣ ⎡ + 2 1 2 1 2 1 T T ) T T (
2. 2C p In ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + 2 1 2 1 T T 2 ) T T (
3. C p In ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + 2 1 2 2 1 T T 4 ) T T (
4. 2C p In ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + 2 1 2 1 T T 4 ) T T (

Correct answer: C p In ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + 2 1 2 2 1 T T 4 ) T T (

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