Which of the following changes decrease the vapour pressure of water kept in a sealed vessel ?
If 1 g of each of the following gases are taken at STP, which of the gases will occupy (a) greatest volume and (b) smallest volume?
$$\mathrm{CO}, \mathrm{H}_2 \mathrm{O}, \mathrm{CH}_4, \mathrm{NO}$$
From Avogadro's law, we know that
Volume of 1 mole of the gas = graw molecular mass $=22.4 \mathrm{~L}$ at STP
Volume occupied by $28 \mathrm{~g} \mathrm{CO}(1 \mathrm{~mol} \mathrm{CO})=22.4 \mathrm{~L}$ at STP
$\left(\because\right.$ Molar mass of $\left.\mathrm{CO}=12+16=28 \mathrm{~g} \mathrm{~mol}^{-1}\right)$
$\therefore \quad$ Volume occupied by $1 \mathrm{~g} \mathrm{~CO}=\frac{22.4}{28} \mathrm{~L}$ at STP
Similarly, volume occupied by $1 \mathrm{~g} \mathrm{~H}_2 \mathrm{O}=\frac{22.4}{18} \mathrm{~L}$ at STP
$\left(\because\right.$ Molar mass of $\left.\mathrm{H}_2 \mathrm{O}=(2 \times 1)+16=18 \mathrm{~g} \mathrm{~mol}^{-1}\right)$
Volume occupied by $1 \mathrm{~g} \mathrm{CH}_4=\frac{22.4}{16} \mathrm{~L}$ at STP
$\left(\because\right.$ Molar mass of $\left.\mathrm{CH}_4=12+(4 \times 1)=16 \mathrm{~g} \mathrm{~mol}^{-1}\right)$
Volume occupied by $1 \mathrm{~g} \mathrm{NO}=\frac{22.4}{30} \mathrm{~L}$ at STP
$\left(\because\right.$ Molar mass of $\left.\mathrm{NO}=14+16=30 \mathrm{~g} \mathrm{~mol}^{-1}\right)$
Thus, $1 \mathrm{~g} \mathrm{CH}_4$ will occupy maximum volume while 1 g of NO will occupy minimum volume at STP.
Physical properties of ice, water and steam are very different. What is the chemical composition of water in all the three states?
Physical properties of ice, water and steam are very different because they found in different states. Ice found in solid, water found in liquid and steam found in vapour states. The chemical composition of water in all the three states (ice, water and steam) is same, i.e., $\mathrm{H}_2 \mathrm{O}$.
The behaviour of matter in different states is governed by various physical laws. According to you, what are the factors that determine the state of matter?
Temperature, pressure, mass and volume are the factors which determine the different states of matter. i.e., solid, liquid and gas.
Use the information and data given below to answer the questions (a) to (c),
Stronger intermolecular forces result in higher boiling point.
Strength of London forces increases with the number of electrons in the molecule.
Boiling point of $\mathrm{HF}, \mathrm{HCl}, \mathrm{HBr}$ and HI are $293 \mathrm{~K}, 189 \mathrm{~K}, 206 \mathrm{~K}$ and 238 K respectively.
(a) Which type of intermolecular forces are present in the molecules HF, $\mathrm{HCl}, \mathrm{HBr}$ and HI ?
(b) Looking at the trend of boiling points of $\mathrm{HCl}, \mathrm{HBr}$ and HI , explain out of dipole-dipole interaction and London interaction, which one is predominant here.
(c) Why is boiling point of hydrogen fluoride highest while that of hydrogen chloride lowest?
From the information and data given in the question, we concluded that
(a) In $\mathrm{HCl}, \mathrm{HBr}$ and HI , dipole-dipole and London forces are present because molecules possess permanent dipole. In HF dipole-dipole, London forces and hydrogen bonding are present.
(b) Electronegativity of chlorine, bromine and iodine decreases in the order are present
$$\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$$
Therefore, dipole moment should decrease from HCl to HI Thus, dipole-dipole interaction should decrease from HCI to HI But boiling point increases on moving from HCl to HI This means that London forces are predominant.
This is so because London forces increases as the number of electrons in a molecule increases and in this case number of electrons is increasing from HCl towards HI
(c) Hydrogen fluoride has highest dipole moment attributes due to highest electronegativity of fluorine as well as presence of hydrogen bonding in HF. Therefore, HF has highest boiling point.