Q Value Of Reaction — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Q-Value of Reaction Applies to nuclear reactions (fission or fusion) where the total mass of the reactants differs from the total mass of the products, allowing mass to be converted into energy. Start with Einstein's mass-energy equivalence principle: E = mc 2 . Apply the law of conservation of energy to a closed nuclear system. Define the energy released (Q) as the difference between the initial and final total energy: Q = E initial - E final . Relate the energy difference to the mass difference ( m = m reactants - m products ). Resulting formula: Q = (m reactants - m products )c 2 . The reaction must be governed by mass-energy equivalence ( E=mc 2 ). The mass defect ( m ) must be calculated using the rest masses of the participating atoms/nuclei. Confusing the Q-value with the total kinetic energy of the resulting particles. Using the atomic numbers (Z) instead of the measured atomic masses (m) in the calculation. Assuming the energy released is proportional to the number of nucleons rather than the calculated mass defect.