Balance the Chemical Equation for the reaction of calcium carbonate with hydrochloric acid: CaCO3+ HCl -> CaCl2 + CO2 + H2O

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To balance chemical equations we need to look at each element individually on both sides of the equation. 

To start with we can add up the elements to see which are unbalanced.


CaCO3 + HCl -> CaCl2 + CO2 + H2O


There is one Calcium atom on the left and one Calcium atom on the right so this is balanced.

There is 1 Carbon atom on the left and 1 Carbon atom on the right so this is balanced.

There are 3 Oxygen atoms on the left and 3 Oxygen atoms on the right so this is balanced.

There is 1 hydrogen atom on the left but 2 on the right so this is unbalanced. Therefore we need to balance it by using 2 molecules of HCl:


CaCO3 + 2HCl -> CaCl2 + CO2 + H2O


Lastly we need to check that the chlorine is balanced, and it is as we can see there are now 2 on each side. Therefore this is now a balanced equation.

Whenever we balance an eqaution you have to change the number of molecules used represented by the big numbers before a molecule e.g 2HCl. You cannot change the subscript (small) numbers as this is the number of each element in a molecule, and you would end up making up your own molecule that doesn't make sense! For example you could not do H2Cl!

The easiest way to balance equations is by going through step by step and each time you make a change- check how it affects the rest of the equation. 

Gemma P. GCSE Biology tutor, GCSE Chemistry tutor, GCSE Maths tutor

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