States of Matter : Gases & Liquids Test - 1

1. In Case of option (a), We have polar ammonia NH₃ but non polar CH₄, tetrahedral and all forces balanced, so weak attraction between the two.

2. Option (B) is correct.
NH₃ is a fairly polar molecules due to the strong electronegativity of N and its pyrimidal shape with a lone pair of electrons at the peak. So two of the molecules have a strong attraction for one another. 

3. In Case of option (c), both molecules being non polar due to symetrical structure in tetrahedrons .

4. In Case of option (d), both molecules are non polar, structure is O=C=O 

Intermolecular force can only be Vaan der Waals force acting between two molecules.

Thermal energy is the energy of a body arising from motion of its atoms or molecules. It is directly proportional to the temperature of the substance. It is the measure of average kinetic energy of the particles of the matter and is thus responsible for movement of particles. This movement of particles is called thermal motion. We have already learnt that intermolecular forces tend to keep the molecules together but thermal energy of the molecules tends to keep them apart. Three states of matter are the result of balance between intermolecular forces and the thermal energy of the molecules.

In a gas, the distance between molecules, whether monatomic or polyatomic, is very large compared with the size of the molecules; thus gases have a low density and are highly compressible.

Density: The molecules of a liquid are packed relatively close together. Consequently, liquids are much denser than gases.

Van der Waals forces are independent of temperature except for dipole-dipole interactions.

Dipole-dipole interaction energy between stationary polar molecules is proportional to 1/ r³ and that between rotating polar molecules is proportional to 1/ r⁶ where ‘r’ is the distance between polar molecules

Besides dipole - dipole interaction, polar molecules can interact by London forces also.

Since, HCl is highly soluble in water, no gas is present in the flask. The pressure exerted is by water vapour which is equal to aqueous tension i.e., 26 mm at 27° C.

London dispersion forces operate only over very short distance. The energy of interaction varies as
1/(distance between two interacting particles)⁶ 

Large or more complex the molecules, greater is the magnitude of London forces.

This is obviously due to the fact that the large electron clouds are easily distorted or polarised.
Hence, greater the polarisability of the interacting particles, greater is the magnitude of the interaction energy.

The formation of hydrogen bonds is an important quality of the water molecules make hydrogen bonds with each other, water takes on some unique chemical characteristics compared to other liquids and, since living things have a high water content, understanding these chemical features is key to understanding life. In liquid water, hydrogen bonds are constantly formed and broken as the water molecules slide past each other.

A hydrogen bond is a partially electrostatic attraction b/w a hydrogen atom which is bound to a more electronegative atom such as N, O and F etc. And also hydrogen bonding occurs only b/w molecules in which H atom bounded to a electronegative atom.

Partial charge is a small charge developed by displacement of electrons. It is less than unit electronic charge and is represented as δ⁺ or δ^–  

HF - Hydrogen bonding HCl,HBr,HI→ Dipole-dipole interaction, London-dispersion force.

It is because of hydrogen bonding . Since F is the most electronegative element , its hydrogen bonding tendency is strongest which makes boiling point of HF increase.