Final answer:
When plaster has a powdery consistency, it is likely due to the chemical reaction of slaked lime in the plaster with carbon dioxide, forming calcium carbonate, necessary for hardening. This differs from industrial processes like the removal of sulfur dioxide from power plant emissions.
Step-by-step explanation:
Areas where plaster has a powdery consistency often indicate a chemical reaction involving the hardening of plaster that contains slaked lime. The pertinent chemical equation involves calcium hydroxide, also known as slaked lime (Ca(OH)2), reacting with carbon dioxide (CO2) to form calcium carbonate (CaCO3), which is a solid that helps in the hardening process of the plaster. This reaction can be seen as:
Ca(OH)2 + CO2 → CaCO3 + H2O
The powdery consistency could be due to the incomplete reaction or degradation of the formed calcium carbonate back into calcium hydroxide and carbon dioxide, often as a result of moisture and environmental conditions. This process is not related to the removal of sulfur dioxide from the flue gas of power plants, which is an entirely different industrial chemical process.