About the Q values , the textbook are using the Q= Δ m c^2 where (Δ m = mass_initial - mass_final). When Q < 0 is endothermic and when Q > 0 is exothermic nuclear process. But i use the another way round , i use the concept of thermodynamics and physical chemistry, Q > 0 is endothermic and Q < 0 when it is exothermic by using (Δ m = mass_final - mass_initial). This is because to let student easily remember and not confusing (although its violate the definition of q value). But i have make the following step when solve q value problem. i) Please state which side of equation. (LHS-RHS or RHS-LHS) ii) State either is exothermic or endothermic iii) State whether the process can occur or not. Magnitude will be the same but the sign is difference. It just like a spectrum concept. E(final)-E(initial)= -ive value (emission spectrum), E(initial)-E(final)= +ive value (emission spectrum). I don't know whether i make any mistakes in my concept or not.