When limestone (solid ) is heated, it decomposes into lime (solid ) and carbon dioxide gas. This is an extremely useful industrial process of great antiquity, because powdered lime mixed with water is the basis for mortar and concrete — the lime absorbs from the air and turns back into hard, durable limestone. Suppose a limekiln of volume is pressurized with carbon dioxide gas to , and heated to . When the amount of has stopped changing, it is found that of have appeared. Calculate the pressure equilibrium constant this experiment suggests for the equilibrium between and at . Round your answer to significant digits. Note for advanced students: it's possible there was some error in this experiment, and the value it suggests for does not match the accepted value.