University:
Cerritos College
Course:
CHEM 112 | General Chemistry
Academic year:

2023
Views:

255

Pages:

2
Author:

p. agatha

Balancing the Reaction Equation Many reactions can be balanced in a try/guess way, but for starters one can follow the steps below. 1. Choose the most complicated chemical formula, set the coefficients the same with 1. 2. Other substances assign temporary coefficients with letters. 3. First, balance the elements that are directly related to the substance that was given coefficient 1. 4. Equalize other elements. It usually helps to balance the O atoms the last. Consider the following examples. Example 1 Write and balance the equation for the reaction between methane gas (CH4 ) and oxygen gas to form carbon dioxide gas and water vapor. Answer:  Step 1 : W rite down the chemical formula and reaction equation: CH4 (g) + O2 (g) CO2 (g) + H2 O(l)  Step 2 : Equalization: a. Set the coefficient CH4 = 1, while the coefficients of other substances are eg letter. 1 CH4 (g) + a O2 (g) b CO2 (g) + c H2 O(l) b. Balance the number of C and H atoms. c. We plug in the coefficients b and c so that the reaction equation becomes: 1 CH4(g) + a O2 (g) 1 CO2 (g) + 2 H2 O(l) d. We balance the number of O atoms. e. The complete balanced reaction equation is: 1 CH4 (g) + 2 O2 (g) 1 CO2 (g) + 2 H2 O(l) Henceforth the coefficient 1 does not need to be written so that the reaction equation becomes: CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2 O(l) (equivalent) Example 2 Write and balance the equation for the reaction between aluminum metal and hydrochloric acid to form aluminum chloride and hydrogen gas. Answer:  Step 1 : Write down the chemical formula and reaction equation: Al(s) + HCl(aq)  AlCl3 (aq) + H2 (g) Step 2 Equalization: a. We set the coefficient AlCl3 = 1, while the coefficients of other substances are exemplified with letters. a Al(s) + b HCl(aq) 1 AlCl3 (aq) + c H2 (g) b. Balance the amount Al We enter a and b into the reaction equation, so the reaction equation becomes: 1 Al(s) + 3 HCl(aq) 1 AlCl3 (aq) + c H2 (g) c. Balance the number of H atoms. We enter the coefficient c, so the reaction equation becomes: 1 Al(s) + 3 HCl(aq) 1 AlCl3 (aq) + 1.5 H2 (g) Because coefficients cannot be fractions, to round off fractions, all coefficients are multiplied by two, so the reaction equation becomes: 2 Al(s) + 6 HCl(aq) 2 AlCl3 (aq) + 3 H2 (g)

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