11th Class Chemistry Thermodynamics

  • question_answer 9) Predict in which of the following, entropy increases/decreases? (i) A liquid crystallizes into a solid. (ii) Temperature of a crystalline solid is raised from 0 K to\[115K.\] (iii) \[2NaHC{{O}_{3}}(s)\to N{{a}_{2}}C{{O}_{3}}(s)+C{{O}_{2}}(g)+{{H}_{2}}O(g)\] (iv)\[{{H}_{2}}(g)\to 2H(g)\]  

    Answer:

    (i) When a liquid crystallizes into a solid, its entropy decreases because degree of randomness is less in a solid as compared to that in a liquid.\[\left( \Delta \text{S }=\text{ }-\text{ }ve \right)\]. (ii) When a crystalline solid is heated from 0 K to 115 K, its entropy increases \[(\Delta S=+ve)\] because at higher temperature, the constituent units start vibration around their mean position. (iii) In the reaction, \[2NaHC{{O}_{3}}(s)\to N{{a}_{2}}C{{O}_{3}}(s)+C{{O}_{2}}(g)+{{H}_{2}}O(g)\] the number of gaseous components are increasing hence the entropy of system will increase. (iv)\[{{H}_{2}}(g)\to 2H(g)\] In above decomposition, number of particles increase therefore, the randomness and entropy will also increase.


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