Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.
The definition of <em>equilibrium</em> is when the forward rate and the reverse rate are <em>equal</em>.
Because in the initial state there's only NO₂, there's no possibility for the reverse reaction (from N₂O₄ to NO₂). Thus the forward rate will be larger than the reverse rate.
Answer: Divide the mass of the object by its volume to yield the density of the object. For example, the object density = mass / (Vf – Vi). Compare the measured density to that of pure gold (19.3 g/cc) to determine whether the object is made of pure gold.
