Which of the following changes is an example of a chemical change?
A. Burning of magnesium ribbon
B. Boiling of water
C. Melting of ice
D. Dissolving sugar in water
Answer: Option A
Solution (By JKExamLibrary)
Burning of magnesium ribbon produces a new substance, magnesium oxide (MgO), and releases heat and light, which are indicators of a chemical change. Melting, dissolving, and boiling are physical changes because the chemical composition remains unchanged. Chemical changes are generally irreversible.
Explanation:
A catalyst does not initiate a reaction; it only changes the rate of a reaction that is already thermodynamically feasible. It provides an alternative pathway with lower activation energy. It does not change the overall enthalpy (ΔH) or the equilibrium position, and it is recovered unchanged in mass.
Explanation:
Ozone decomposes quickly to O₂, leaving no residual disinfectant. Thus a small chlorine dose may be added after ozonation for distribution protection. Chlorine provides residual protection.
Explanation:
The Ostwald process is the industrial method for manufacturing nitric acid (HNO₃). It involves the catalytic oxidation of ammonia (NH₃) to nitric oxide (NO), which is then further oxidized to nitrogen dioxide (NO₂) and absorbed in water to form concentrated nitric acid.
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