Chapter 17, Problem 17A.1ST

Interpretation Introduction

Interpretation:

The partial pressure for the species in the reaction $\text{2NOBr(g) }\stackrel{}{\to }{\text{ 2NO(g) + Br}}_{\text{2}}\text{(g)}$ has to be calculated.

Concept Introduction:

Partial pressure:

The total pressure exerted by a mixture of gases is the sum of the partial pressure of component gases.

    ${\text{P}}_{\text{tot}}{\text{= P}}_{\text{1}}{\text{+ P}}_{\text{2}}{\text{+P}}_{\text{3}}{\text{+P}}_{\text{4}}\mathrm{.......}\text{= }{\displaystyle \sum _{\text{i=1}}^{\text{n}}{\text{P}}_{\text{i}}}$

Explanation of Solution

Given equation is:

    $\text{2NOBr(g) }\stackrel{}{\to }{\text{ 2NO(g) + Br}}_{\text{2}}\text{(g)}$

${\text{NOBr is decomposed so its partial pressure falls from p}}_{\text{o}}{\text{ to (p}}_{\text{o}}\text{-Δp)}$.  2 moles of $\text{NOBr}$ decomposes to give 2 moles of ${\text{NO}}_{\text{2}}$, then the partial pressure of ${\text{NO}}_{\text{2}}$ increases from ${\text{p}}_{\text{o}}\text{to 2Δp}$.  Partial pressure of ${\text{Br}}_{\text{2}}$ also increases from ${\text{p}}_{\text{o}}\text{to Δp}$.

$\begin{array}{l}\underset{\_}{\begin{array}{l}{\text{ p(NOBr) p(NO) p(Br}}_{\text{2}}\text{) p}\\ {\text{Initially p}}_{\text{o}}{\text{ 0 0 p}}_{\text{o}}\\ {\text{Later p}}_{\text{o}}{\text{-Δp 2Δp Δp p}}_{\text{o}}\text{+ 2Δp}\end{array}}\\ \text{Equivalent to }\frac{3}{2}{\text{p}}_{\text{o}}-\frac{1}{2}\text{p p}-{\text{p}}_{\text{o}}\frac{1}{2}\text{(p}-{\text{p}}_{\text{o}})\\ \end{array}$