Question

a chemist measures the energy change \\( \delta h \\) during the following reaction:

\\( 2 \mathrm { hgo } ( s ) \
ightarrow 2 \mathrm { hg } ( l ) + \mathrm { o } _ { 2 } ( g ) \quad \delta h = 182. \mathrm { kj } \\)

use the information to answer the following questions.

this reaction is...	\\( \bigcirc \\) endothermic. \\( \bigcirc \\) exothermic.
if you said heat will be released or absorbed in the second part of this question, calculate how much heat will be released or absorbed. be sure your answer has the correct number of significant digits.	\\( \square \mathrm { kj } \\)

Explanation:

Step1: Determine the type of reaction

Since $\Delta H = 182\ \text{kJ}>0$, the reaction is endothermic (heat is absorbed).

Step2: Calculate the moles of HgO

The molar mass of HgO ($M$) is $M = 200.59 + 16=216.59\ \text{g/mol}$.
The number of moles of HgO ($n$) is $n=\frac{m}{M}=\frac{88.9\ \text{g}}{216.59\ \text{g/mol}}\approx0.410\ \text{mol}$.

Step3: Relate moles of HgO to heat change

From the balanced equation $2\ \text{mol}$ of HgO reacting has $\Delta H = 182\ \text{kJ}$.
Let $x$ be the heat change for $0.410\ \text{mol}$ of HgO.
Using proportion: $\frac{x}{0.410\ \text{mol}}=\frac{182\ \text{kJ}}{2\ \text{mol}}$.
$x=\frac{182\ \text{kJ}\times0.410\ \text{mol}}{2\ \text{mol}} = 37.3\ \text{kJ}$

Answer:

• This reaction is endothermic.
• Yes, absorbed.
• $37.3\ \text{kJ}$