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Answer: Balance the Chemical Equation

Saturday, 16 of February , 2008 at 11:05 am

Question: Balance the chemical equation using Linear Algebra.

CO + CO_2 + H_2 ~~\rightarrow ~~ CH_4 + H_2O

Answer: In order to balance the chemical equations, we need to find the five unknowns (ab,c,d,e).

aCO + bCO_2 + cH_2 ~~\rightarrow ~~ dCH_4 + eH_2O

Since the number of chemical elements are conserved, we know that:

C: a+b=d
O: a+2b=e
H: 2c=4d + 2e

\therefore we need to solve the following linear system.

 \left( \begin{array}{ccccc}1 & 1 & 0 & -1 & 0 \\1 & 2& 0 & 0 & -1 \\0 & 0 & 2 & -4 & -2 \end{array} \right)\left( \begin{array}{c}a \\b\\c \\d \\e \end{array} \right) = \left( \begin{array}{c}0 \\0\\0 \end{array} \right)

This system of equations can easily be solved with Maple.

> with(Student[LinearAlgebra]):
> A := Matrix([[1, 1, 0, -1, 0, 0],
		[1, 2, 0, 0, -1, 0],
		[0, 0, 2, -4, -2, 0]]):
> ReducedRowEchelonForm(A)

According to maple, we can reduce the linear system to:

 \left( \begin{array}{ccccc}1 & 0 & 0 & -2 & 1 \\0 & 1& 0 & 1 & -1 \\0 & 0 & 1 & -2 & -1 \end{array} \right)\left( \begin{array}{c}a \\b\\c \\d \\e \end{array} \right) = \left( \begin{array}{c}0 \\0\\0 \end{array} \right)

According to the above equation, we don’t have a unique solution. However, we know that the linear system will have a solution \forall d,e \in \mathbb R where

a = 2d -e
b = -d +e
c = 2d+e

Since we know that a,b,c,d,e \in \mathbb N (where 0 \notin  \mathbb N), we can add additional constraints to our linear system. If we look at the above equations, it is easy to see that the following constraint must hold:

2d > e > d

Using the linear system and the above constraint, we find the following solutions…

CO + CO_2 + 7H_2 ~~\rightarrow ~~ 2CH_4 + 3H_2O
2CO + CO_2 + 10H_2 ~~\rightarrow ~~ 3CH_4 + 4H_2O
CO + 2CO_2 + 11H_2 ~~\rightarrow ~~ 3CH_4 + 5H_2O
3CO + CO_2 + 13H_2 ~~\rightarrow ~~ 4CH_4 + 5H_2O
2CO + 2CO_2 + 14H_2 ~~\rightarrow ~~ 4CH_4 + 6H_2O
CO + 3CO_2 + 15H_2 ~~\rightarrow ~~ 4CH_4 + 7H_2O
4CO + CO_2 + 16H_2 ~~\rightarrow ~~ 5CH_4 + 6H_2O

As you can see, there is still an infinite amount of solutions for this chemical equations. Some can be reduced, however majority of the equations can’t be reduced

Category: Answers, Linear Algebra

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