For each chemical reaction listed in the first column of the table below, predic

Question

For each chemical reaction listed in the first column of the table below, predict the sign (positive or negative) of the reaction entropy Delta S_rxn. If it's not possible to decide with the information given, check the "not enough information" button in the last column. Note for advanced students: Assume the temperature remains constant. Assume gases and solutions are ideal. Cao (s) + Co_2 (g) rightarrow CaCO_3 (s) Delta S_rxn 0 not enough information. NaCl (s) rightarrow Na^- (aq) + Cl^-(aq) Delta S_rxn 0 not enough information. Ag^+ (aq) + Cl^- (aq) rightarrow AgCl(s) Delta S_rxn 0 not enough information.

Explanation / Answer

Ans. Under specified condition, the entropy (degree of randomness or freedom to move) of gas phase > liquid phase > solid phase.

#A. dSrxn < 0 ;

The reactants, solid CaO and gaseous CO2 forms a solid product. So, the entropy of gaseous CO2­ decreases during the reaction (gas phase converted to solid phase).

Therefore, overall, entropy of the reaction decreases because reactants has molecules in gaseous phase but the product has all molecules in solid state.

#B. dSrxn > 0

Dissociation of solid NaCl (No molecules of NaCl can move in a crystal of NaCl kept on the table) into Na+ and Cl- ions increases the entropy of reaction. Because solvated Na+ and Cl- can move through solution much very much faster compared to the same in a solid.

#C. dSrxn < 0

Formation of solids from the solvated ions decreases the entropy. Solvated ions have freedom to move through the solution, but no freedom of movement in solid state- so entropy decreases.

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