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Calculate the internal energy change in each of the following cases : (i) A system absorbs 15 kJ of heat and does 5 kJ of work. (ii) 5 kJ of work is done on the system and 15 kJ of heat is given out by the system. |
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Answer» (i) Here, q = +15 kJ w = – 5 kJ ∴ According to first law of thermodynamic ΔU = q + w = 15 + (–5) = 10 kJ Thus, internal energy of the system increases by 10 kJ (ii) Here, w = + 5 kJ q = – 5 kJ ∴ According to first law of thermodynamics, ΔU = q + w = – 15 + (+ 5) = – 10 kJ Thus, the internal energy of the system decreases by 10 kJ. |
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