Q Value Nuclear Reaction Calculator
Enter reactant and product atomic masses to calculate the Q-value (energy released or absorbed) in a nuclear reaction using E=Δmc².
Use the Q Value Nuclear Reaction Calculator
Reaction Masses
Enter reactant and product masses,
then click Calculate Q-Value.
Mass Balance
Formula Applied
Q = Δm × 931.494 MeV/u
Q = u × 931.494 MeV/u
Summary
The Q-value of a nuclear reaction is the net energy released (positive Q) or absorbed (negative Q) during the process. It is computed from the difference in total rest mass between reactants and products using Einstein's mass-energy equivalence: Q = (M_reactants − M_products) × 931.494 MeV/u. A positive Q indicates an exothermic (energy-releasing) reaction such as fission or fusion; a negative Q indicates an endothermic reaction that requires an energy input to proceed.
How it works
- Enter the atomic masses of all reactant nuclei in atomic mass units (u).
- Enter the atomic masses of all product nuclei in atomic mass units (u).
- The calculator sums the total reactant mass and total product mass.
- It computes the mass difference: Δm = M_reactants − M_products.
- Q is obtained by multiplying Δm by the conversion factor 931.494 MeV/u.
- Results are shown in MeV, keV, and joules alongside an exo/endothermic label.
Use cases
- Verify whether a proposed nuclear fusion or fission reaction releases energy.
- Determine the threshold energy needed to drive an endothermic nuclear reaction.
- Cross-check textbook Q-value problems in nuclear physics courses.
- Evaluate the energy yield of alpha, beta, or gamma decay processes.
- Design nuclear reaction chains in reactor physics studies.
- Confirm mass balance in particle physics reaction equations.