Which reaction below is a physical change? a. CH4​(g) + 2O2​(g) → CO2​(g) + 2Hs​O(l)
b. CaO(s) + H2​O(l)→ Ca(OH)2​(s)
c. H2​O (l) → H2​O(s)
D. 2Hs​O (l) → 2H2​(g) + O2​(l)

c. H₂​O (l) → H₂​O(s)

Explanation:

The correct answer is option C: The molecular formulas for the substance(s) on the left side of the equation and on the right side of the equation are identical. This means that there was not a chemical change, but a physical one.

In this concrete example, what happened was a change of states of matter: from liquid (l) to solid (s).

Other reactions have different molecular formulas on both sides of the equation, thus they represent chemical changes.

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> b takes place in the gas phase in an isothermal tubular reactor. the feed is one mole of a per one mole of c, an inert. the entering temperature and pressure are 427°c and 10 atm, respectively. the gas constant r = 0.08206 atm · l/mol · k.