Heat and Thermodynamics 5 Question 38
39. During the melting of a slab of ice at $273 K$ at atmospheric pressure
(1998, 2M)
(a) positive work is done by the ice-water system on the atmosphere
(b) positive work is done on the ice-water system by the atmosphere
(c) the internal energy of the ice-water increases
(d) the internal energy of the ice-water system decreases
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Answer:
Correct Answer: 39. (b, c)
Solution:
- There is a decrease in volume during melting on an ice slab at $273 K$. Therefore, negative work is done by ice-water system on the atmosphere or positive work is done on the ice-water system by the atmosphere. Hence, option (b) is correct.
Secondly heat is absorbed during melting (i.e., $d Q$ is positive) and as we have seen, work done by ice-water system is negative ( $d W$ is negative). Therefore, from first law of thermodynamics $d U=d Q-d W$
change in internal energy of ice-water system, $d U$ will be positive or internal energy will increase.
