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### Course: Class 10 Chemistry (India)>Unit 1

Lesson 2: Balancing a chemical reaction

# Balancing another combustion reaction

A balanced chemical equation shows the same number of each type of atom on both sides of the arrow. In this example, we balance the combustion reaction of ethane, C₂H₆.

## Want to join the conversation?

• Do the letters in parentheses make a difference? i.e.: (g)
• Yes, they tell you what state the substance is in. That matters a great deal in how the substance behaves in general and how it participates in the reaction in particular.
• How are the oxygens balanced at the end? It looks like you end up with 7 on one side and 14 on the other.
• As another note, bear in mind that in the final "balanced" reaction, the presenter messed up and accidentally wrote C2H2, not C2H6.
• i did the reaction on paper before he started and got 1 C2H2 + 8 O2 = 2 Co2 + 6 H2O. what did i do wrong? it's all balanced and everything.
• The equation is actually....
C2H6 + O2 ===> Co2 + H2O.
Whereas you have written C2H2 in your equation. Hence, a different result.
• did sal just change the subscript value of the hydrogen in the rewritten reaction @
• Sal wrote C2H2 by mistake. he actually maent C2H6
• So when someone says "CO2" it is C*O2 and not (CO) squared, correct? (I know it isn't a mathematical equation, just relating)
• Yes you are correct @Ryan McHale, the numbers that are in between the molecular formula, or in other words, in between the "letters" are the number of that particular atom that is behind the number, and it's not actually written just like that... It is in the subscript, like the opposite area of where you write the Indices in Mathematics which means a little bit below the letter.

The letter (element) that has a number written in the subscript of it will be the number of atoms of that particular element, and the number that is written normally before the whole molecule, is the number of that particular molecule in the equation! So for `CO2`, there are 1 Carbon, and 2 Oxygen atoms and for `2 CO2`, there are 2 molecules of Carbon dioxide, so altogether we would have 2 Carbon, and 4 Oxygen atoms. Hope this helps!
• You can multiply an element by a decimal to balance an equation?
• Only if the final stoceometric ratio is in whole numbers.
• At their are fourteen oxygen but then at the last oxygen he only has twelve. Did he do something wrong OR do I just not understand.
• If you mean for the very last equation, there are 14 oxygens atoms on both sides. The reactant side has 7O2 which is 14 oxygen atoms (7x2=14). The product side has 4CO2 which is 8 oxygen atoms (4x2=8) and 6H2O which is 6 oxygen atoms for a total of 14 oxygen atoms (8+6 =14).

Hope that helps.
• When I tried to balance this reaction on my own, I got:

4C2H6 + 14O2 --> 8CO2 + 12H20

If I wrote that instead of what Sal had at , would I still get credit? Thanks!
• You may get partial credit but it isn’t correct because you can divide all your coefficients by 2 to get what Sal got. The correct balanced equation always has the lowest whole number coefficients.
• hiya everyone ~
I'm curious, why don't we just leave it at fractional molecules when working out and not putting the experiment into practice ? Even if it's sort of "weird" looking but why do we change it ??
i do understand that in practice it would be weird, but on paper??
thank you so much for helping, appreciated!! ~
• Molecules come in whole number amounts. Even though the equation is balanced with a coefficient of 3.5 for O2, it implies that we have 0.5 of a molecule of O2. It doesn’t really make sense to have half a molecule.

Sometimes chemical equations will be written with fractional coefficients which works mathematically, but not so much in a chemistry context where we know whole number molecules are what actually is happening.

Hope that helps.