Question

Predict the sign of \(\Delta S\) for the following: (a) a lake freezing (b) ice cream thawing (c) a candle burning (d) weeding a garden

Short answer

Question: Predict the sign of the change in entropy (ΔS) for each of the following processes: (a) a lake freezing, (b) ice cream thawing, (c) a candle burning, and (d) weeding a garden. Answer: (a) negative, (b) positive, (c) positive, (d) negative

Step-by-step solution

(a) A lake freezing

When a lake freezes, the water molecules become more ordered as they arrange themselves into a solid ice structure. This process results in a decrease in entropy, so the sign of ΔS will be negative. Thus, the change in entropy is negative: \(\Delta S < 0\).

(b) Ice cream thawing

As ice cream thaws, the solid ice cream and ice crystals within it become a more disordered liquid. This process results in an increase in entropy, so the sign of ΔS will be positive. Thus, the change in entropy is positive: \(\Delta S > 0\).

(c) A candle burning

When a candle burns, the solid wax and the oxygen molecules in the surrounding air are transformed into more disordered gaseous products like carbon dioxide and water vapor. Additionally, the chemical reaction releases heat, which increases the disorder of the surrounding molecules. These factors result in an increase in entropy, so the sign of ΔS will be positive. Thus, the change in entropy is positive: \(\Delta S > 0\).

(d) Weeding a garden

Weeding a garden involves removing unwanted plants and making the garden more orderly and organized. This process results in a decrease in entropy (more order). Note that the plants themselves undergo no change in entropy, but the appearance of the garden and the arrangement of the plants become more ordered. Therefore, the sign of ΔS will be negative. Hence, the change in entropy is negative: \(\Delta S< 0\). To summarize, the sign of ΔS for each process is: (a) A lake freezing: negative (b) Ice cream thawing: positive (c) A candle burning: positive (d) Weeding a garden: negative