# How do you balance nuclear fission equations?

Jul 16, 2014

The sums of the superscripts and of the subscripts must be the same on each side of the equation.

Here are some links that show how to balance nuclear equations.

http://socratic.org/questions/how-do-you-balance-nuclear-equations?source=search

http://socratic.org/questions/how-do-you-complete-and-balance-nuclear-equations?source=search

http://socratic.org/questions/can-you-write-a-balanced-nuclear-equation-for-the-alpha-decay-of-ra-226?source=search

http://socratic.org/questions/what-balanced-equation-represents-nuclear-fusion

EXAMPLE

Complete the following equation for the fission of uranium-235.

$\text{_92^235"U" + _0^1"n" → _56^142"Ba" + ? + 3 _0^1"n}$

Solution

On the left hand side, sum of subscripts = 92 + 0 = 92
On the right hand side, sum of subscripts = 56 + $Z$ + 3(0) = 56 + $Z$
$Z$ = 92 – 56 = 36

On the left hand side, sum of superscripts = 235 + 1 = 236
On the right hand side, sum of superscripts = 142 + $A$ + 3(1) = 145 + $A$
$A$ = 236 – 145 = 91

The symbol for a nucleus is ""_Z^AX.

The element with $Z$ = 36 is krypton.

Thus, the unknown nucleus is $\text{_36^91"Kr}$.

The balanced nuclear equation is

$\text{_92^235"U" + _0^1"n" → _56^142"Ba" + _36^91"Kr" + 3 _0^1"n}$