The Van der Waal's constant "a" is a correction factor to...

The Van der Waal's constant "a" is a correction factor to the ideal gas law for the intermolecular attractions within a substance. List 1 contains the substances and List 2 contains the values of "a" $\left(\mathrm{L}^{2} \mathrm{~atm} \mathrm{~mol}^{2}\right)$. $$\begin{array}{ll} {\text { List-1 }} & {\text { List-2 }} \\ \hline \text { (i) } \mathrm{C}_{6} \mathrm{I} \mathrm{I}_{6}(\mathrm{~g}) & \text { (a) } 0.217 \\ \text { (ii) } \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{3}(\mathrm{~g}) & \text { (b) } 5.464 \\ \text { (iii) } \mathrm{Ne}(\mathrm{g}) & \text { (c) } 18.000 \\ \text { (iv) } \mathrm{I}_{2} \mathrm{O}(\mathrm{g}) & \text { (d) } 24.060 \end{array}$$ Which of the following combinations represents the correct matching of the substance with the corresponding "a" value. (1) i-a ii-d $\mathrm{iii}-\mathrm{c} \quad \mathrm{iv}-\mathrm{b}$ $\begin{array}{llll}\text { (2) } i-b & \text { ii }-c & \text { iii-a } & \text { iv }-d\end{array}$ $\begin{array}{llll}\text { (3) } i-c & \text { ii }-d & \text { iii }-a & \text { iv }-b\end{array}$ (4) $\mathrm{i}-\mathrm{d}$ $\begin{array}{lll}\text { ii }-a & i i i-b & \text { iv }-c\end{array}$

The Van der Waal's constant "a" is a correction factor to the ideal gas law for the intermolecular attractions within a substance. List 1 contains the substances and List 2 contains the values of "a" $\left(\mathrm{L}^{2} \mathrm{~atm} \mathrm{~mol}^{2}\right)$.
$$\begin{array}{ll}
{\text { List-1 }} & {\text { List-2 }} \\
\hline \text { (i) } \mathrm{C}_{6} \mathrm{I} \mathrm{I}_{6}(\mathrm{~g}) & \text { (a) } 0.217 \\
\text { (ii) } \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{3}(\mathrm{~g}) & \text { (b) } 5.464 \\
\text { (iii) } \mathrm{Ne}(\mathrm{g}) & \text { (c) } 18.000 \\
\text { (iv) } \mathrm{I}_{2} \mathrm{O}(\mathrm{g}) & \text { (d) } 24.060
\end{array}$$
Which of the following combinations represents the correct matching of the substance with the corresponding "a" value.
(1) i-a ii-d $\mathrm{iii}-\mathrm{c} \quad \mathrm{iv}-\mathrm{b}$
$\begin{array}{llll}\text { (2) } i-b & \text { ii }-c & \text { iii-a } & \text { iv }-d\end{array}$
$\begin{array}{llll}\text { (3) } i-c & \text { ii }-d & \text { iii }-a & \text { iv }-b\end{array}$
(4) $\mathrm{i}-\mathrm{d}$
$\begin{array}{lll}\text { ii }-a & i i i-b & \text { iv }-c\end{array}$

Key Concepts

Molecular Size and Polarizability

Molecular size and polarizability are key factors in determining the magnitude of intermolecular attractions. Larger and more polarizable molecules tend to have stronger dispersion forces due to a larger electron cloud, which can lead to a higher 'a' value. This concept helps explain variations in the constant among different substances as observed in the Van der Waals correction.

Intermolecular Attractions

Intermolecular attractions refer to the forces that act between molecules, such as London dispersion forces, dipole-dipole interactions, and hydrogen bonding. In the context of gases, these forces affect how closely molecules can approach each other, thereby influencing properties like pressure and phase behavior.

Van der Waals Equation

The Van der Waals equation is an adjustment of the ideal gas law that accounts for the finite size of molecules and the intermolecular forces acting between them. It introduces correction factors to accommodate real gas behavior, particularly under conditions of high pressure and low temperature, where deviations from ideal behavior become significant.

Correction Factor 'a'

The 'a' constant in the Van der Waals equation represents the correction for intermolecular attractions. It quantitatively adjusts for the attractive forces between gas particles, which, if uncorrected, would lead to an overestimation of the pressure exerted by the gas. A higher 'a' value implies stronger attractive forces among the molecules.

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