Question

What mass of calcium oxide results from decomposition of a $200g$ mass of calcium carbonate?

Answer 1

Hint: In this question, we first need to write the balanced chemical equation of reaction and then we have to find the number of moles of calcium oxide using stoichiometric calculations which correctly interpret the relation between reactants and products. Further, the moles of reactant can be converted into products to get the final answer.

Complete answer:
A decomposition reaction can be defined as the chemical reaction in which a single reactant breaks down into two or more products. Generally, a decomposition reaction can be represented as follows:
$AB\to A+B$
Where, $AB$ is the reactant or parent molecule while $A$ and $B$ are the products of the reaction.
Decomposition reaction of calcium carbonate is an example of thermal decomposition. When calcium carbonate i.e., $CaC{{O}_{3}}$ is heated, it decomposes to form calcium oxide $(CaO)$ and carbon dioxide $(C{{O}_{2}})$. This process is widely used in industries for the manufacturing of quick lime. The balanced chemical reaction involved in this process is as follows:
$CaC{{O}_{3}}\xrightarrow{\Delta }CaO+C{{O}_{2}}$
Now, interpreting mole ratio on the basis of stoichiometric coefficients to find the number of moles of calcium oxide as follows:
As per question, mass of calcium carbonate $=200g$
Molar mass of calcium carbonate $=100.08\ gmo{{l}^{-1}}$
Number of moles of calcium carbonate considered in the reaction $n=\dfrac{\text{given mass}}{\text{molar mass}}$
$\Rightarrow n=\dfrac{200}{100.08}$
$\Rightarrow n=1.99$
Since, 1 mole of $CaC{{O}_{3}}$ decomposes to form $\Rightarrow $ 1 mole of $CaO$
Therefore, 1.99 moles of $CaC{{O}_{3}}$ will be decomposed to form $\Rightarrow $ 1.99 mole of $CaO$
Now, molar mass of calcium oxide $=56\ gmo{{l}^{-1}}$
And we know the number of moles of any substance $n=\dfrac{\text{given mass}}{\text{molar mass}}$.
Hence, the mass of calcium oxide formed after the reaction is as follows:
Mass of $CaO$ formed $=$ number of moles $\times $molar mass
$\Rightarrow {{m}_{CaO}}=56\times 1.99$
$\Rightarrow {{m}_{CaO}}=111.4g$
Thus, on decomposition of 200g of calcium carbonate, 111.4 g of calcium oxide is formed.

Note:
It is important to note that the chemical equation must contain the lowest whole number coefficients before comparing the stoichiometry of the reactants and products. Also remember that stoichiometry is the coefficient of reactants and products and not the composition of atoms in a compound and make sure to set up proper conversion factors to avoid calculation mistakes.