Magnesium carbonate, MgCO3\text{MgCO}_3MgCO3, decomposes when heated to form magnesium oxide, MgO\text{MgO}MgO, and carbon dioxide gas, CO2\text{CO}_2CO2.
MgCO3→MgO+CO2\text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2MgCO3→MgO+CO2
If 21.0 g21.0\text{ g}21.0 g of magnesium carbonate decomposes to make 10.0 g10.0\text{ g}10.0 g of magnesium oxide, what mass of carbon dioxide gas is produced?