A 100-mL sample of water is placed in a coffee cup calorimeter. When 1.0 g of an

Question

A 100-mL sample of water is placed in a coffee cup calorimeter. When 1.0 g of an ionic solid is added, the temperature decreases from 21.5 degree C to 20.8 degree C as the solid dissolves. For the dissolving of the solid a. Delta H 0 c. Delta S(system) 0 e. none of these The dissolution of ammonium nitrate occurs spontaneously in water at 25 degree C. As NH_4NO_3 dissolves the temperature of the water decreases. What are the signs of Delta_r H, Delta_r S, and Delta_r G for this process? a. Delta_r H > 0, Delta_r S 0 b. Delta_r H > 0, Delta_r S > 0, Delta_r G > 0 c. Delta_r H > 0, Delta_r S > 0, Delta_r G

Explanation / Answer

18) when ionic solid is dissolved and temperature decreased it means we have endothermic reaction ( i.e heat is absorbed , dH > 0). Entropy of dissoling system > 0 . We have dS surrounding = - dH / T . SInce we get +ve dH it means dS surrounding is neagtive which means dS surrounding < 0 . Ds universe =0 , Hence option none of

18- Option E

19) dH > 0 , dS > 0 , dGo < 0

option C

20) we have relation dGo = dHo - TdSo ,

when dHo is +ve and dSo is -ve we always get dGo a +ve value.

This means reaction will be never spontaneous since sponatneous means we should get dGo -ve

Hence option E

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