Question

A mercury mirror forms inside a test tube as a result of the thermal decomposition of mercury(ii) oxide: 2 hgo(s) → 2 hg(l) + o2(g) δhrxn = 181.6 kj (a) how much heat is needed to decompose 996 g of the oxide?

Answer 1

Answer : The amount of heat needed to decompose 996 g of the oxide is, 416.8 kJ

Explanation :  Given,

Mass of $HgO$ = 996  g

Molar mass of $HgO$ = 216.59 g/mol

First we have to calculate the moles of HgO.

$\text{Moles of }HgO=\frac{\text{Mass of }HgO}{\text{Molar mass of }HgO}=\frac{996g}{216.59g/mole}=4.59mole$

Now we have to calculate the heat required.

The balanced chemical reaction is:

$2HgO(s)\rightarrow 2Hg(l)+O_2(g)$

From the given chemical reaction we conclude that,

As, 2 moles of HgO required heat for decomposition = 181.6 kJ

So, 4.59 moles of HgO required heat for decomposition = $\frac{4.59}{2}\times 181.6=416.8kJ$

Therefore, the amount of heat needed to decompose 996 g of the oxide is, 416.8 kJ