Nathan R. answered 02/26/13
Renaissance man and Polymath who enjoys mentoring as much as learning
We want the number of each element on the Reactants (Left side) to be equal to the number of each element on the Product side (Right side). So lets begin with the Reactants
When you count the number of each element of the reactants you get:
Mgreactant = 1 (from MgO)
Creactant = 1 (from CO2)
Oreactant =3 (1 from MgO and 2 from CO2)
Then you count the number of each element of the product you get:
Mgproduct = 1 (from MgCO3)
Cproduct = 1 (from MgCO3)
Oproduct = 3 (from MgCO3)
Then compare the totals for each element
Mgreactant = 1 ; Mgproduct = 1 :conclusion ---> no change
Creactant = 1 ; Cproduct = 1 :conclusion ---> no change
Oreactant = 3 ; Oproduct = 3 :conclusion ---> no change
Since there was no imbalance your question becomes your answer.
If there was an imbalance found, you would adjust the Coefficient (the number in front of each compound or element) until the count for the element on both the reactant and product side are equal.
For example; the equation Mg + N2 ---> Mg3N2 when we start to balance the Mg we get the following:
Mgreactant = 1 (from elemental Mg) and Mgproduct = 3 (from Mg3N2)
1 : 3 ---> since they don't equal each other you must increase the coefficient of the reactant to 3
3Mg + N2 ---> Mg3N2
↑ Since 3Mg is equivalent to Mg3 and the N2 are balanced already the final equation is this equation