Q value (nuclear science)

In nuclear physics and chemistry, the Q value for a nuclear reaction is the amount of energy absorbed or released during the reaction. The value relates to the enthalpy of a chemical reaction or the energy of radioactive decay products. It can be determined from the masses of reactants and products:

${\displaystyle Q=(m_{\text{r}}-m_{\text{p}})\times \mathrm {0.9315~GeV/Da} ,}$

where ${\displaystyle m_{\text{r}}}$ and ${\displaystyle m_{\text{p}}}$ are the sums of the reactant and product masses.

Q values affect reaction rates. In general, the larger the positive Q value for the reaction, the faster the reaction proceeds, and the more likely the reaction is to "favor" the products.