No, it is not true that a gram of uranium contains 20 billion calories. Calories are units of energy commonly used to quantify the energy content of food and other substances. The energy content of uranium is typically measured in terms of its nuclear potential energy or the energy released through nuclear reactions.
To provide some context, the energy released by nuclear reactions is usually expressed in units of joules (J) or electron volts (eV) rather than calories. Uranium is primarily known for its use as a fuel in nuclear reactors, where it undergoes nuclear fission, releasing a significant amount of energy.
The energy released by a gram of uranium through nuclear fission is on the order of millions of times greater than the energy released through a chemical reaction or combustion process. However, it is not accurate to directly equate this energy to calories, as the conversion factors between nuclear energy and calorie units are not straightforward due to the fundamental differences in the underlying processes.
In summary, while uranium possesses a tremendous amount of energy potential, it is not meaningful to express it in terms of calories.