Question

Calculate the amount of carbon dioxide gas and calcium oxide (quicklime) formed during the decomposition of 25g of calcium carbonate(limestone)

Answer 1

The balanced chemical equation for the decomposition reaction of calcium carbonate (CaCO₃) to form carbon dioxide (CO₂) and calcium oxide (CaO) is:

${\mathrm{CaCO}}_3\left(\mathrm{s}\right)\to \mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

The total mass of the products and reactants should be calculated first. (atomic mass of Ca=40 , O=16 ,C=12)

• The atomic mass of CaCO₃= 40 + 12 + (3X16) = 100g
• The atomic mass of CaO = 40 + 16 = 56g
• The atomic mass of CO₂ = 12 + (2X16) = 44g

Let's write the mass equation for the decomposition of CaCO₃

$100\mathrm{g}\to 56\mathrm{g}+44\mathrm{g}$

• 100g of CaCO₃ decomposes to give 56g of CaO and 44g of CO₂
• Let's assume like, that 25g of CaCO₃ decomposes to give xg of CaO

$$\begin{gathered} 100\mathrm{g}\to 56\mathrm{g} \\ 25\mathrm{g}\to \mathrm{xg} \end{gathered}$$ (cross multiplication is done here)

let's calculate the xg like this:

$$\begin{gathered} 100\mathrm{g}\mathrm{X}\hspace{0.17em}\mathrm{xg}=56\mathrm{g}\mathrm{X}25\mathrm{g} \\ \mathrm{xg}=(56\mathrm{X}\hspace{0.17em}25)/100 \\ =14\mathrm{g} \end{gathered}$$

So 25g of CaCO₃ decomposes to give 14g of CaO

Similarly, let's calculate the mass of C. Assume the mass of CO₂ as xg

$$\begin{gathered} 100\mathrm{g}\to 44\mathrm{g} \\ 25\mathrm{g}\to \mathrm{xg} \end{gathered}$$ (cross multiplication is done here)

Let's calculate the xg like this:

$$\begin{gathered} 100\mathrm{g}\mathrm{X}\hspace{0.17em}\mathrm{xg}=44\mathrm{g}\mathrm{X}\hspace{0.17em}25\mathrm{g} \\ \mathrm{xg}=(44\mathrm{X}25)/100 \\ =11\mathrm{g} \end{gathered}$$

So 25g of CaCO₃ decomposes to give 11g of CO₂

The decomposition of 25g of CaCO₃ gives 11g of CO₂ and 14g of CaO.