Balancing Chemical Reaction Question

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My question when it comes to balancing chemical equations, is that I know that we have to write down the number of atoms per element, but after we achieve that, when does the coefficient come into the equation and what is the significance of that coefficient.

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The coefficient essentially means that you have that many of that molecule, i.e. 4H2O means I have 4 molecules of H2O and therefore, 8 molecules of H and 4 molecules of O in total. You use coefficients to balance out atoms such as if you have 4CO2 on one side and O2 on the other side, you might give O2 a coefficient of 4 to balance out the O.