Question

Predict the sign of the entropy change,Delta S, for each of the following reactions:The signs are either going to be pos or negativea) Pb^2+(aq) + 2Cl-(aq) ---> PbCl2(s)b) CaCO3(s) ---> CaO(s) + CO2 (g)c) 2NH3(g) ---> N2(g) + 3H2(g)d) P4(g) + 5O2(g) ---> P4O10(s)e) C4H8(g) + 6O2(g) ---> 4CO2(g) + 4H2O(g)f) I2(s) ---> I2(g)

Answer 1

Answer: a)
`Pb^(2+)(aq)+2Cl^-(aq)\rightarrow PbCl_2(s)`: negative

b)
`CaCO_3(s)\rightarrow CaO(s)+CO_2(g)` : positive

c)
`2NH_3(g)\rightarrow N_2(g)+3H_2(g)`: positive.

d)
`P_4(g)+5O_2(g)\rightarrow P_4O_(10)(s)` : negative

e)
`C_4H_8(g)+6O_2(g)\rightarrow 4CO_2(g)+4H_2O(g)`: positive.

f)
`I_2(s)\rightarrow I_2(g)` : positive.

Step-by-step explanation:

Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.

`\Delta S` is positive when randomness increases and
`\Delta S` is negative when randomness decreases.

a)
`Pb^(2+)(aq)+2Cl^-(aq)\rightarrow PbCl_2(s)`

As ions are moving to solid form , randomness decreases and thus sign of
`\Delta S` is negative.

b)
`CaCO_3(s)\rightarrow CaO(s)+CO_2(g)`

As solid is changing to gas, randomness increases and thus sign of
`\Delta S` is positive.

c)
`2NH_3(g)\rightarrow N_2(g)+3H_2(g)`

As 2 moles of reactants are converted to 4 moles of products , randomness increases and thus sign of
`\Delta S` is positive.

d)
`P_4(g)+5O_2(g)\rightarrow P_4O_(10)(s)`

As gas is changing to solid, randomness decreases and thus sign of
`\Delta S` is negative.

e)
`C_4H_8(g)+6O_2(g)\rightarrow 4CO_2(g)+4H_2O(g)`

As 7 moles of reactants are converted to 8 moles of products , randomness increases and thus sign of
`\Delta S` is positive.

f)
`I_2(s)\rightarrow I_2(g)`

As solid is changing to gas, randomness increases and thus sign of
`\Delta S` is positive.