Major Points• Balancing Chemical Reactions (reactions occur, but oftentimes the equation does not work out without some balancing)
• Balancing Chemical Reactions Using Information From Word Problems (balancing the equations by extracting information from a word problem) What do the symbols behind the compounds in a reaction mean?You will see symbols in parentheses such as (s), (g), (l), and (aq) behind elements in an unbalanced chemical reaction.
These symbols simply tell you what state of matter the element or compound is in at the time. s= solid g= gas l= liquid aq= aqueous (dissolved in water) Tip: When making an equation out of a word problem, pick out words such as "combine" or "in the presence of" to denote the elements in the reactant side of the equation. Words like "form" and "produce" can tell you which elements are the products of the reaction. |
Example Problems1. Balance this equation: Pb(C2H3O2)2 + KI ---> PbI2 + KC2H3O2
Answer: Pb(C2H3O2)2 + 2KI ---> PbI2 + 2KC2H3O2 2. Balance this equation: MnO2 + C ---> Mn + CO2 Answer: This equation is already balanced. 3. Balance this equation: N2O3 + H2O ----> HNO2 Answer: N2O3 + H2O ----> 2HNO2 4. Use the word problem to make a balanced chemical equation: Glass is a mixture of several compounds, but a major constituent of most class is calcium silicate, CaSiO3. Glass can be etched by treatment with hydrogen fluoride: HF attacks the calcium silicate of the glass, producing gaseous and water-soluble products (Which can be removed by washing the glass). For example, the volumetric glassware in chemistry laboratories is often graduated by suing this process. Balance the equation for the reaction of hydrogen fluoride with calcium silicate. CaSiO3 (s) + HF (g) ---> CaF2 (aq) + SiF4 (g) + H2O Answer: CaSiO3 + 6HF ---> CaF2 + SiF4 + 3H2O |
Balancing the Equations
Balancing chemical reactions is mainly a process of trial and error. You may try many times to balance an equation, but the answer may be elusive for a while as you try to come up with the correct sequence of numbers that will allow the equation to be true.
Our example will be FeCl3 + KOH ---> Fe(OH)3 + KCl
As you can tell, the number of each element that appears on the reactant side of the problem does not correspond with the number of each element that appears on the product side. That's how we can tell that we need to balance this equation. We need to make the number of each element be the same on one side as it is on the other.
As you try to balance these reactions, you may find it helpful to keep a chart much like the one pictured below:
Our example will be FeCl3 + KOH ---> Fe(OH)3 + KCl
As you can tell, the number of each element that appears on the reactant side of the problem does not correspond with the number of each element that appears on the product side. That's how we can tell that we need to balance this equation. We need to make the number of each element be the same on one side as it is on the other.
As you try to balance these reactions, you may find it helpful to keep a chart much like the one pictured below:
I've created a table with a REACTANTS column and a PRODUCTS column. Also pictured are the different elements found throughout the equation. We will use this table to keep track of the numbers of each element on each side of the equation. When the numbers on both the reactant side and the product side match, we know we've successfully balanced an equation.
Now that we have our chart, we will get to work on balancing the equation. This step is hard to describe because there are so many ways to approach balancing the equation. I suggest re-writing the equation putting little spaces for numbers so that you'll have room to test out numbers in front of each element or compound. (Something that looks like this– ___ –in front of each element or compound.
Your equation should now look like this: __ FeCl3 + __ KOH ----> __ Fe(OH)3 + __ KCl
Begin putting numbers in the slots while filling in the chart we made before. Try to balance out the equation using trial and error.
When you are done, your chart should look like this:
Your equation should now look like this: __ FeCl3 + __ KOH ----> __ Fe(OH)3 + __ KCl
Begin putting numbers in the slots while filling in the chart we made before. Try to balance out the equation using trial and error.
When you are done, your chart should look like this:
If your chart looks like that, then your equation should read: FeCl3 + 3 KOH ----> Fe(OH)3 + 3KCl
The ratio for this equation would be 1:3:1:3
Remember, if you ever come to an opportunity to SIMPLIFY your answer, do so. In this case, we will not simplify because nothing can be divided by the same number. If we came up with an answer such as one with a ratio of 2:4:4:2, we would know to simplify it to 1:2:2:1, because all the numbers can be divided by 2.
That is the process that you should go through in order to balance an equation! Good luck!
The ratio for this equation would be 1:3:1:3
Remember, if you ever come to an opportunity to SIMPLIFY your answer, do so. In this case, we will not simplify because nothing can be divided by the same number. If we came up with an answer such as one with a ratio of 2:4:4:2, we would know to simplify it to 1:2:2:1, because all the numbers can be divided by 2.
That is the process that you should go through in order to balance an equation! Good luck!
Tip: While balancing equations, try to fix hydrogen and oxygen LAST! Balance other elements first.
Online Resources
How Can I Balance an Equation? (made by a chemistry teacher, so some of the stuff is directed towards the class, but still helpful): http://misterguch.brinkster.net/eqnbalance.html
Balancing Equations Alternate Strategies: http://preparatorychemistry.com/Bishop_Balancing_Equations_help.htm
Balancing Equations Alternate Strategies: http://preparatorychemistry.com/Bishop_Balancing_Equations_help.htm
Video Resources
Balancing Chemical Equations: http://www.youtube.com/watch?v=UGf60kq_ZDI&feature=related
Balancing The Equations (By Me!): https://vimeo.com/53905806
Balancing Chemical Equations With Chloe: http://www.youtube.com/watch?v=3NEh-jdwVTQ
Balancing The Equations (By Me!): https://vimeo.com/53905806
Balancing Chemical Equations With Chloe: http://www.youtube.com/watch?v=3NEh-jdwVTQ
Activity Resources
Balancing Act!: http://education.jlab.org/elementbalancing/index.html
Balancing Chemical Equations Worksheet: http://misterguch.brinkster.net/equationworksheets.html (click the 7th worksheet)
Balancing Chemical Equations Worksheet: http://misterguch.brinkster.net/equationworksheets.html (click the 7th worksheet)