Chapter 15, Problem 1DE

(a)

Interpretation Introduction

To determine:

The gas or gases whose concentration can be monitored by using a spectrophotometer.

Answer to Problem 1DE

Solution:

The concentration of iodine gas can be monitored with the spectrometer.

Explanation of Solution

The spectrometer is a device which splits light into the array of separate colors which is shown as a spectrum on the spectrometer.

The gases which absorb in the visible region can only be monitored by the spectrometer. Since iodine gas lies in the visible region and gives violet color so, the concentration of iodine gas can be monitored with the spectrometer.

(b)

Interpretation Introduction

To determine:

The way to determine the extinction coefficient for the given substance.

Answer to Problem 1DE

Solution:

The extinction coefficient is calculated by the slope of absorbance versus concentration graph.

Explanation of Solution

The absorbance of the given solution is calculated by using the formula,

$A=\epsilon bc$

Where,

• $A$ is the absorbance of the solution.
• $\epsilon$ is the extinction coefficient.
• $b$ is the path length of the solution.
• $c$ is the concentration of the solution.

Therefore, the plot of $A$ versus $c$ gives slope equals to the $b\cdot \epsilon$ . The path of the solution is known and hence, the extinction coefficient can be calculated.

(c)

Interpretation Introduction

To determine:
The experiment to calculate the equilibrium constant at $600\text{K}$ .

Answer to Problem 1DE

Solution:

The sample containing an equal concentration of hydrogen and iodine is used to determine the equilibrium constant of the reaction.

Explanation of Solution

The balanced chemical equation for the given reaction is,

${\text{H}}_2\left(g\right)+{\text{I}}_2\left(g\right)\to 2\text{HI}\left(g\right)$

The equilibrium constant of the given reaction is calculated by using the formula,

$K_{\text{c}}=\frac{{\left[\text{HI}\right]}^2}{\left[{\text{H}}_2\right]\left[{\text{I}}_2\right]}$

The experiment that can be performed to calculate the equilibrium constant for the given reaction is to determine the absorbance of the sample solution containing equal concentrations of hydrogen and iodine which can be used to calculate the concentration of given solution.

(d)

Interpretation Introduction

To determine:

The enthalpy of the given reaction by using the bond enthalpy values.

Answer to Problem 1DE

Solution:
The enthalpy of the given reaction is $-11\text{kJ/mol}$ .

Explanation of Solution

The balanced chemical equation for the given reaction is:

${\text{H}}_2\left(g\right)+{\text{I}}_2\left(g\right)\to 2\text{HI}\left(g\right)$

The enthalpy of the given reaction is calculated by using the formula,

$\begin{array}{c}\Delta H={\displaystyle \sum E_{\text{Bonds}\text{broken}}}-{\displaystyle \sum E_{\text{Bonds}\text{formed}}}\\ =E\left(\text{H}-\text{H}\right)+E\left(\text{I}-\text{I}\right)-2E\left(\text{H}-\text{I}\right)\end{array}$

Substitute the values of $E\left(\text{H}-\text{H}\right)$ , $E\left(\text{I}-\text{I}\right)$ and $E\left(\text{H}-\text{I}\right)$ in the above equation.

$\begin{array}{c}\Delta H=436\text{kJ/mol}+151\text{kJ/mol}-2\times 299\text{kJ/mol}\\ =-11\text{kJ/mol}\end{array}$

(e)

Interpretation Introduction

To determine:
If the value of $K_{\text{c}}$ at $600\text{K}$ is smaller or larger than that of the value at $300\text{K}$ .

Answer to Problem 1DE

Solution:
The value of the equilibrium constant at $300\text{K}$ is larger than the value at $600\text{K}$ .

Explanation of Solution

The value of enthalpy of the reaction is negative as the answer in part (d) which means the energy is released in the given reaction. Therefore, the increase in temperature results in the shifting of equilibrium in backward direction. Thus, the value of equilibrium constant declined by increasing temperature.