Helium atom is two times heavier than a hydrogen molecule. At 298 K, the average kinetic energy…

Problem: Helium atom is two times heavier than a hydrogen molecule. At 298 K, the average kinetic energy of a Helium atom is

(A) two times that of hydrogen molecule

(B) same as that of a hydrogen molecule

(C) four times that of a hydrogen molecule

(D) half that of a hydrogen molecule

Ans: (B)

Solution: The average kinetic energy of an atom is given as $\large \frac{3}{2}k T $

Hence , It does not depend on mass of the atom.

If for two gases of molecular weights MA and MB at temperature TA and TB …

Problem : If for two gases of molecular weights MA and MB at temperature TA and TB, TA MB = TB MA , then which property has the same magnitude for both the gases.

(A) density

(B) pressure

(C) KE per mol

(D) Vrms

Ans: (D)

Sol:(i) Density of gas $\large \rho = \frac{P M}{R T} $

Since $\large \frac{M_B}{T_B} = \frac{M_A}{T_A} $

Hence , at the same pressure $\large \rho_A = \rho_B$

But if pressure is different then $\large \rho_A \ne \rho_B$

(ii) Pressure of the gases would be equal if their densities are equal other wise not.

(iii) KE per mol $\large = \frac{3}{2}R T$

It will be different for the two gases.

(iv) $\large V_{rms} = \sqrt{\frac{3RT}{M}}$

Since $\large \frac{T_B}{M_B} = \frac{T_A}{M_A} $

Vrms of A = Vrms of B

At 100 degree C and 1 atm, if the density of liquid water is 1.0 g/cc and that of water vapour is 0.0006 g/cc…

Problem : At 100 °C and 1 atm , if the density of liquid water is 1.0 g/cc and that of water vapour is 0.0006 g/cc, then the volume occupied by water molecule in one litre of steam at that temperature is

(A) 6 cc

(B) 60 cc

(C) 0.6 cc

(D) 0.06 cc

Ans: (C)

Solution: Mass of 1 lt water vapour = V × d = 1000 × 0.0006 = 0.6 g

Volume of liquid water = 0.6/1 = 0.6 cc

The circulation of blood in human body supplies O2 and releases CO2. the concentration…

Problem : The circulation of blood in human body supplies O2 and releases CO2. the concentration of O2 and CO2 is variable but on an average, 100 ml blood contains 0.02 g of O2 and 0.08 g of CO2. The volume of O2 and CO2 at 1 atm and at body temperature 37 °C, assuming 10 lt blood in human body, is

(A) 2 lt, 4 lt

(B) 1.5 lt, 4.5 lt

(C) 1.59 lt, 4.62 lt

(D) 3.82 lt, 4.62 lt

Ans: (C)

Solution: 100 ml blood has 0.02 g O2 and 0.08 g CO2

10,000 ml blood has 2 g O2 and 8 g CO2

using PV = nRT

for O2, $\large 1 \times V_{O_2} = \frac{2}{32} \times 0.0821 \times 310 $

= 1.59 litre

for CO2 , $\large 1 \times V_{CO_2} = \frac{8}{44} \times 0.0821 \times 310 $

= 4.62 litre