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Homework Help: How can I balance an Equation?

  1. Jan 28, 2010 #1
    1. The problem statement, all variables and given/known data

    Ok, please use my example of giving me a step by step guide on how to balance an equation:


    2. Relevant equations
    K + Br2 --> KBr


    3. The attempt at a solution

    I know that I should write down the equation, draw a line underneath the arrow to seperate the balancing. Then add up the atoms for each side..but I am stuck now. What is the rest of the steps to take to balance out this equation?


    Thanks.
     
  2. jcsd
  3. Jan 28, 2010 #2
    Ok, so you write down the skeleton equation. That's good. Now you want to balance it. To do this, you need to count the atoms on each side for potassium and bromine. On both the left and right side of the equation, there is only one molecule of potassium each. This means that potassium is balanced. For bromine, there are two atoms of bromine on the left side of the equation, but only one atom on the right side. Therefore, you need to increase the bromine atoms on the right side of the equation. Simply place a '2' in front of KBr. Now count the number of bromine atoms on each side of the equation. '2' and '2'. Bromine is balanced, but now potassium is unbalanced because the left side of the equation has only one potassium atom whereas the right side has two. You need to increase the potassium atoms, so just put a two in front of potassium on the left side of the equation. Now potassium is balanced with two atoms on both sides of the equation. The final equation should look something like this:

    2K + 2Br2 → 2KBr

    For balancing other equations, perform a similar procedure that I have outlined. Try balancing the following equations and send me a message with your answers and I'll help you if they are wrong or tell you if they are right.

    - H2+ O2 → H2O
    - C + H2→ CH4
    - N2 + H2 → NH3

    And here is a bonus question.
    - C3H8+ O2→ CO2+ H2O

    I hope this helps.

    *note - the numbers behind atoms are all subscript
     
    Last edited: Jan 28, 2010
  4. Jan 29, 2010 #3
    Could you please give me a step by step guide so I can answer them correctly :P

    i.e.

    1. Write down the unbalanced equation.

    2. etc

    3. etc

    4. etc

    Thanks :)
     
  5. Jan 29, 2010 #4

    Char. Limit

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    Gold Member

    Actually, he did. It's in the first paragraph.

    Now, try to solve them, and send him (or her, hard to tell online) your answers.

    Examples to solve, you need those to understand.

    Try it first, then tell us where you get stuck.
     
  6. Jan 29, 2010 #5

    Borek

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    Staff: Mentor

  7. Jan 29, 2010 #6
    Ok, so let me get this right;

    1. Write down the unbalanced equation.

    2. You now need to count the atoms on each side.
    On both the left and right side of the equation, there is only one molecule of potassium each. This means that potassium is balanced. For bromine, there are two atoms of bromine on the left side of the equation, but only one atom on the right side.

    3. You need to increase the bromine atoms on the right side of the equation.

    4. Simply place a '2' in front of KBr.

    5. Now count the number of bromine atoms on each side of the equation. '2' and '2'.

    6. Bromine is balanced, but now potassium is unbalanced because the left side of the equation has only one potassium atom whereas the right side has two.

    7. You need to increase the potassium atoms, so just put a two in front of potassium on the left side of the equation.

    8. Now potassium is balanced with two atoms on both sides of the equation. The final equation should look something like this:

    2K + 2Br2 → 2KBr


    That is the step by step guide, right?
     
  8. Jan 29, 2010 #7

    Char. Limit

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    Gold Member

    Except you put an unnecessary 2 coefficient on the bromine
    molecule. Since it wasn't in your process, I don't know how it got there.
     
  9. Jan 29, 2010 #8
    Yes it is, but I saw a mistake on my part. The final equation is 2K + Br2 → 2KBr.

    Sorry about that.
     
  10. Jan 29, 2010 #9

    Char. Limit

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    Gold Member

    There you go. That's it.

    Now try the others.
     
  11. Jan 30, 2010 #10
    Ehh...

    Bonus question answer I think..

    5 O2→ + C3H8 ==> 3 CO2 + 4 H2O
     
  12. Jan 30, 2010 #11
    First question: 2 H2 + O2 ==> 2 H2O
     
  13. Jan 30, 2010 #12

    Borek

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    Staff: Mentor

    So far, so good. Nitpickers will tell you you have put two arrows in the propane combustion one.
     
    Last edited by a moderator: Aug 13, 2013
  14. Jan 30, 2010 #13
    Ahh right.

    Thanks a lot for the help.

    I do have some more questions because it's all just confusing me :P
     
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