A chemical change involves a transformation that alters the composition of substances, resulting in the formation of new substances.
Among the equations provided:
- 2H2 + O2 → 2H2O - This is a chemical change, as hydrogen and oxygen react to form water.
- ^219_86Rn → ^215_84Po + α - This is also a chemical change; it involves the radioactive decay of radon into polonium and an alpha particle.
- H2O(s) → H2O(g) - This is a physical change (sublimation) because it changes from solid to gas without altering the chemical composition of water.
- C2H5OH(l) → C2H5OH(g) - This is again a physical change (evaporation) where ethanol changes from liquid to gas.
Therefore, both the first and second equations show chemical changes. If you have to choose only one, you can select either:
- 2H2 + O2 → 2H2O (combination reaction). OR
- ^219_86Rn → ^215_84Po + α (radioactive decay).
If the question expects just one response, then the first one is typically the most straightforward example of a chemical change due to bond formation and breaking.