Question

Without doing any calculations, determine the sign of ΔSsys for each of the following chemical reactions: 2H2S9(g)+ 3O2(g) --->2H2O(g) + 2SO2(g), 2H30(aq) + CO3(aq) ----> CO2 + 3H2O(l), mg(s) + cl2(g) ---> MgCl2(s), HCl(g) + NH3(g) ---> NH4Cl(s)

Answer 1

(a)

2H2S9(g)+ 3O2(g) --->2H2O(g) + 2SO2(g)

In the above reaction, total number of gaseous moles of product are 4, while those of reactants are 5.

Since number of gaseous moles decrease, so hence the entropy change is negative.

(b)

2H₃O⁺(aq) + CO₃-(aq) ----> CO₂(g) + 3H₂O(l)

Here, number of gaseous moles of the system have increased, so the entropy increases which means dS is positive.

(c)

Mg(s) + Cl2(g) ---> MgCl2(s)

Here, number of gaseous moles of the system have decreased, so the entropy decreases which means dS is negative.

(d)

HCl(g) + NH3(g) ---> NH4Cl(s)

Here also, number of gaseous moles of the system have decreased, so the entropy decreases which means dS is negative.