Answer the following questions:
Are the equations of nuclear reactions (such as those given in Section 13.7) ‘balanced’ in the sense a chemical equation (e.g., ) is? If not, in what sense are they balanced on both sides?
(a) Nuclear reaction equations are NOT balanced in the same sense as chemical equations. In chemical reactions, mass is strictly conserved. However, in nuclear reactions, while the number of protons and neutrons is conserved, the total mass is not conserved. Nuclear reactions are balanced in the sense that mass-energy is conserved on both sides, as expressed by: Q = (sum of initial masses - sum of final masses)c².
If both the number of protons and the number of neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice-versa) in a nuclear reaction?
(b) Although the number of nucleons (protons and neutrons) is conserved, the mass is not conserved. The nuclear mass is always less than the total mass of its individual constituents due to mass defect. The difference in binding energies between reactants and products results in a mass difference, which is converted to energy (or vice-versa) through Einstein's mass-energy relation: ΔE = ΔMc².
A general impression exists that mass-energy interconversion takes place only in nuclear reaction and never in chemical reaction. This is strictly speaking, incorrect. Explain.
(c) Mass-energy interconversion occurs in ALL processes, including chemical reactions. However, energies associated with nuclear processes are about a million times larger than chemical processes. Due to this, the mass change in chemical reactions is extremely small and practically negligible, creating the incorrect impression that mass-energy conversion does not occur in chemical reactions.
Explanation
This question tests understanding of conservation laws in nuclear vs chemical reactions. Part (a) clarifies that nuclear reactions conserve nucleon number but not mass, unlike chemical reactions. Part (b) explains that mass defect and binding energy differences enable mass-energy conversion. Part (c) addresses the misconception by noting that nuclear energies are ~million times larger, making chemical mass changes negligible but not absent.