In a nuclear reactor, each atom of uranium (of atomic mass 235 u) releases about 200 MeV when it fissions. What is the change in mass when 2.60 kg of uranium-235 is fissioned?

0.002372187708 kg

Explanation:

Each atom of Uranium 235 releases 200 MeV = 200*10⁶*1.60218*10⁻¹⁹

= 200*1.60218*10⁻¹³ Joule

Number of atoms in a 2.6 kg sample mass = (2.6/0.235) * 6.02214076*10²³

⇒Number of atoms in a 2.6 kg sample mass = 66.627*10²³ atoms

Change in energy = Change in mass / (speed of light) ²

ΔE = Δmc²

⇒200*1.60218*10⁻¹³*66.627*10²³ = Δm * (3*10⁸) ²

⇒Δm = 200*1.60218*10⁻¹³*66.627*10²³ / (3*10⁸) ²

⇒Δm = 2372.187708*10⁻⁶ kg

∴Change in mass = 0.002372187708 kg