To balance the equation Fe + HNO3 = Fe(NO3)3 + NO2 + H2O using the algebraic method step-by-step, you must have experience solving systems of linear equations. The most common methods are substitution/elimination and linear algebra, but any similar method will work.
Step 1: Label Each Compound With a Variable
Label each compound (reactant or product) in the equation with a variable to tướng represent the unknown coefficients.
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a Fe + b HNO3 = c Fe(NO3)3 + d NO2 + f H2O
Step 2: Create a System of Equations
Create an equation for each element (Fe, H, N, O) where each term represents the number of atoms of the element in each reactant or product.
Fe: 1a + 0b = 1c + 0d + 0f H: 0a + 1b = 0c + 0d + 2f N: 0a + 1b = 3c + 1d + 0f O: 0a + 3b = 9c + 2d + 1f
Step 3: Solve For All Variables
Use substitution, Gaussian elimination, or a calculator to tướng solve for each variable.
- 1a - 1c = 0
- 1b - 2f = 0
- 1b - 3c - 1d = 0
- 3b - 9c - 2d - 1f = 0
Use your graphing calculator's rref() function (or an online rref calculator) to tướng convert the following matrix into reduced row-echelon-form:
[ 1 0 -1 0 0 0] [ 0 1 0 0 -2 0] [ 0 1 -3 -1 0 0] [ 0 3 -9 -2 -1 0]
The resulting matrix can be used to tướng determine the coefficients. In the case of a single solution, the last column of the matrix will contain the coefficients.
Simplify the result to tướng get the lowest, whole integer values.
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- a = 1 (Fe)
- b = 6 (HNO3)
- c = 1 (Fe(NO3)3)
- d = 3 (NO2)
- f = 3 (H2O)
Step 4: Substitute Coefficients and Verify Result
Count the number of atoms of each element on each side of the equation and verify that all elements and electrons (if there are charges/ions) are balanced.
Fe + 6 HNO3 = Fe(NO3)3 + 3 NO2 + 3 H2O
Since there is an equal number of each element in the reactants and products of Fe + 6HNO3 = Fe(NO3)3 + 3NO2 + 3H2O, the equation is balanced.