balnced equation CaCO3-->CaO+CO2

how many moles of CO2 are produced if you start with 3 mol of CaCO3?

The equation tells you that 1 mole CaCO3 = 1 mole CaO = 1 mole CO2; therefore, 3 moles CaCO3 will produce 3 moles of both CaO and CO2.

OR you can use the dimensional approach this way,
3 moles CaCO3 x (1 mole CO2/1 mole CaCO3) = 3 moles CO2. The numbers in the factor within the parentheses come from the balanced equation.

To determine the number of moles of CO2 produced when starting with 3 mol of CaCO3, we need to use the balanced equation:

CaCO3 -> CaO + CO2

According to the equation, for every 1 mol of CaCO3, 1 mol of CO2 is produced. Therefore, the ratio of CaCO3 to CO2 is 1:1.

Since we have 3 mol of CaCO3, we can say that 3 mol of CO2 will be produced. This is based on the 1:1 ratio of the balanced equation.