• # 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)${{H}_{2}}(g)\to 2H(g)$

(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.