How can a cup of tea and a gallon of tea that are at the sane temperature have different thermal energies?

A cup of tea and a gallon of tea at the same temperature can have different thermal energies due to their differing volumes and masses. Thermal energy is proportional to the amount of substance present; thus, the larger volume of the gallon of tea contains more molecules, which collectively store more thermal energy. Consequently, while both may be at the same temperature, the gallon has significantly more thermal energy because it has a greater mass.