Question

For the following reactions, indicate whether the entropy of the system increases, decreases, or remain nearly the same.

a) Al3+ (aq) + 3 OH- (aq) --> Al(OH)3 (s)

b) CaCO3 (s) --> CaO (s) + CO2 (g)

c) Mg (s) + Cu2+ (aq) --> Mg2+ (aq) + Cu (s)

d) 6 CO2 (g) + 6 H2O (g) --> C6H12O6 (s) + 6 O2

Answer 1

Entropy : the measure of disorder of a system is called entropy.It is a state property so we can measure change in entropy(dS).

a)

Al3+ (aq) + 3 OH- (aq) --> Al(OH)3 (s)

From above reaction the 1 mole of Al+3 and 3 moles OH-particles are free in aqueous solution so entropy is high but in produt side it is converted to solid so disorderness become low, Hence Entropy decreases from reactant to products.

b)

CaCO3 (s) --> CaO (s) + CO2 (g)

From the above reaction the 1 mole of solid particles are converted to 2 moles of gaseous particles so diorderness increases so Entropy increases.

c)

Mg (s) + Cu2+ (aq) --> Mg2+ (aq) + Cu (s)

From above reaction both are the same charge ions so entropy remains constant

d)

6 CO2 (g) + 6 H2O (g) --> C6H12O6 (s) + 6 O2 (g)

From the above reaction the 6 moles of CO2 gas and 6 moles of H2O gas particles are converted into 1 mole of solid particles so disorderness of the system decreases hence entropy decreases.