27.3 - Nuclear reactions

Comparing nuclear and chemical reactionsA nuclear reaction is any process that changes the nucleus of an atom. Nuclear reactions may change one element into another or change one isotope into a different isotope of the same element. Because nuclear reactions involve the strong nuclear force, the energy is typically a millions times greater compared to chemical reactions. Chemical reactions rearrange shared electrons but do not change the nucleus. Read the text aloud
Writing balanced nuclear reaction equations
Nuclear reactions can change an element into a different element by altering the number of protons and neutrons. Nuclear reactions are represented by nuclear reaction equations, just as chemical reactions are represented by chemical reaction equations. Every nuclear reaction equation has two parts: reactants and products. Consider the nuclear reaction that produces carbon-14 in the atmosphere. In this nuclear reaction, a neutron interacts with nitrogen-14 to produce carbon-14 and a proton. The equation for this reaction is
(27.3) n 0 1 + N 7 14 Reactants C 6 14 + p 1 1 Products
Balancing rules for nuclear reaction equationsA correct nuclear equation must show mass balance by having the mass numbers equal on both sides of the equation. First, this means that the total number of protons plus neutrons must be the same before the reaction and after the reaction. Second, the total charge before the reaction must equal the total charge afterward, which is the basic law of charge conservation. These two fundamental rules for balancing nuclear reaction equations can be used to determine an unknown element in a reaction. Read the text aloud
Consider the incomplete reaction equation n 0 1 + U 92 235 X Z A + S 38 94 r+ n 0 1 + n 0 1 To find the unknown element X we start by applying the charge conservation (proton balance) rule:
92 = Z + 38 ⇒ Z = 54
From the periodic table we see that the element with atomic number 54 is xenon. Next we identify the xenon isotope by applying the mass balance rule:
1 + 235 = A + 94 + 1 + 1 ⇒ A = 140
So the unknown nucleus is xenon-140 or X 54 140 e . The complete reaction is n 0 1 + U 92 235 X 54 140 e+ S 38 94 r+ n 0 1 + n 0 1 Read the text aloud
In a 1917 experiment, Rutherford bombarded a nitrogen-14 nucleus with a helium-4 nucleus (an alpha particle), causing the nitrogen atom to change to a different element and producing a proton. What was the resulting isotope of his reaction? Show

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