Question

Predict the sign of the entropy change for each of the following processes and give your reasoning why:

1. Solid sugar is added to water to form a solution.

2. Iodine vapor condenses on a cold surface to form crystals.

3. N₂(g) + 3H₂(g) 2 NH₃(g)

4. H₂O(l) H₂O(g)

5. CaCO₃(s) CaO(s) + CO₂(g)

6. NH₄NO₃(s) + H₂O(l) NH₄⁺(aq) + NO₃^-(aq)

Please let me know why for each questions

Answer 1

Entropy is the measure of disorderness of the system.

Gas molecules are more disordered than liquid molecules , solid molecules and liquid molecules are more disordered than solid.

Therefore, order of entropy is

gas > liquid > solid

Examples:

- When solid is converted to liquid or gas, entropy increases. Sign of entropy = + ve

-When gas is converted to liquid or solid, entropy decreases. Sign of entropy = - ve

- When liquid is converted to gas, entropy increases. Sign of entropy = + ve

- When liquid is converted to solid, entropy decreases. Sign of entropy = - ve

1) Solid sugar is added to water to form a solution.

Conversion of solid to liquid , so entropy increases.

  Sign of entropy = + ve

2) Iodine vapor condenses on a cold surface to form crystals.

Convesion of gas to solid , so entropy decreases.

Sign of entropy = - ve

3) N₂(g) + 3H₂ (g) ---> 2 NH₃(g)

4 moles of gas molecules ----> 2 moles of gas molecules

4 moles of gas molecules converted into 2 moles of gas molecules , means decrease in no of gas molecules.

Therefore, decrease in entropy.

Sign of entropy = - ve

4) H₂O(l) ------> H₂O(g)

water is converted into vapor.

i,e. conversion of liquid to gas. So entropy increases.

Sign of entropy = + ve

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

1 mole of solid -----------> 1 mole of solid 1 mole of gas

Therefore, addition of gas molecules to the system. So entropy increases.

Sign of entropy = + ve

6) NH₄NO₃(s) + H₂O(l) ---------> NH₄⁺ (aq) + NO₃^- (aq)

1mole of solid 1 mole of liquid 1 mole of aq.solution 1 mol of aq.solution

Therefore, addition liquid molecules to the system. So entropy increases.

( liquid + liquid system is more disordered than solid + liquid system because of more no of liquid molecules in iquid + liquid system than in solid + liquid system)

Sign of entropy = + ve