Question

Mixing of which of the following pair of components involve significant energy change?

• A. Sulphur, Water
• B. Sulphur, Iron filings
• C. Calcium carbonate, Sulphur
• D. Potassium, Ice cold water

Answer 1

The correct option is D

Potassium, Ice cold water

Explanation of the correct option:

Potassium (K) reacts violently even with cold Water (H₂O) and produces a large quantity of heat along with Potassium hydroxide (KOH) and Hydrogen (H₂) gas.

$$\begin{gathered} 2\mathrm{K}\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 2\mathrm{KOH}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)+\mathrm{Heat} \\ \left(\mathrm{Potassium}\right)(\mathrm{Ice}\mathrm{Cold}\mathrm{Water})(\mathrm{Potassium}\mathrm{hydroxide})\left(\mathrm{Hydrogen}\right) \end{gathered}$$

This reaction involves significant energy change as there is a lot of heat production when Potassium and Ice cold water react.

Explanation of incorrect options:

(a) Sulphur, Water: On mixing Sulphur (S) with water, sulphur just floats on the surface of water and no reaction occurs between them.

(b) Sulphur, Iron filings: On mixing Sulphur with Iron (Fe) filings, a mixture is formed and there is no reaction.

(c) Calcium carbonate, Sulphur: On mixing Calcium carbonate (CaCO₃) with Sulphur, there is no reaction.

Hence, option (d) is correct.