States Of Matter(11th And 12th > Chemistry ) Questions and answers for exam Preparation

11th And 12th > Chemistry

STATES OF MATTER MCQs

Total Questions : 30 | Page 1 of 3 pages

If $C_{1}, C_{2}, C_{3}$ .........represent the speeds of $n_{1}, n_{2}, n_{3}$ ......... molecules, then the root mean square speed is _____.

$\frac{\sqrt{n_{1} {C_{1}}^{2} + n_{2} {C_{2}}^{2} + n_{3} {C_{3}}^{2} + . . .}}{n_{1} + n_{2} + n_{3} + . . .}$
$\frac{{⟮ n_{1} {C_{1}}^{2} + n_{2} {C_{2}}^{2} + n_{3} {C_{3}}^{2} + . . ⟯}^{\frac{1}{2}}}{n_{1} + n_{2} + n_{3} + . . . . .}$
$\frac{{⟮ n_{1} {C_{1}}^{2} ⟯}^{\frac{1}{2}}}{n_{1}} + \frac{{⟮ n_{2} {C_{2}}^{2} ⟯}^{\frac{1}{2}}}{n_{2}} + \frac{{⟮ n_{3} {C_{3}}^{2} ⟯}^{\frac{1}{2}}}{n_{3}} + . . . . .$
$⟮ \frac{{⟮ n_{1} C_{1} + n_{2} C_{2} + n_{3} C_{3} + . . . ⟯}^{2}}{⟮ n_{1} + n_{2} + n_{3} + . . . . . ⟯} ⟯^{\frac{1}{2}}$

Discuss Question

Answer: Option A. ->

\frac{\sqrt{n_{1} {C_{1}}^{2} + n_{2} {C_{2}}^{2} + n_{3} {C_{3}}^{2} + . . .}}{n_{1} + n_{2} + n_{3} + . . .}

:
A

Root mean square speed = $\frac{\sqrt{n_{1} {C_{1}}^{2} + n_{2} {C_{2}}^{2} + n_{3} {C_{3}}^{2} + . . .}}{n_{1} + n_{2} + n_{3} + . . .}$

Question 2.

The ratio of the rate of diffusion of helium and methane under identical condition of pressure and temperature will be___.

Discuss Question

Answer: Option B. -> 2
:
B

$\frac{r_{H e}}{r_{C H_{4}}} = \sqrt{\frac{M_{C H_{4}}}{M_{H e}}} \Rightarrow \sqrt{(} \frac{16}{4}) \Rightarrow 2$

Question 3.

The temperature at which RMS velocity of $S O_{2}$ molecules is half that of He molecules at 300 K is

150 K
600 K
900 K
1200 K

Discuss Question

Answer: Option D. -> 1200 K
:
D

$\frac{U_{S O_{2}}}{U_{H} e} = \frac{1}{2} = \sqrt{\frac{M_{H e}}{M_{S O_{2}}} \frac{T_{S O_{2}}}{T_{H e}}} = \sqrt{\frac{4}{64} \frac{T_{S O_{2}}}{300}}$

$= \frac{4}{64} \frac{T_{S O_{2}}}{300} = \frac{1}{4}; T_{S O_{2}} = 1200^{\circ} K$

Question 4.

Helium atom is two times heavier than a hydrogen molecule at 298 K, the average kinetic energy of helium is

Two times that of a hydrogen molecule
Same as that of a hydrogen molecule
Four times that of a hydrogen molecule
Half that of a hydrogen molecule

Discuss Question

Answer: Option B. -> Same as that of a hydrogen molecule
:
B

$\frac{E_{H e}}{E_{H_{2}}} = \sqrt{\frac{T_{H_{e}}}{T_{H_{2}}}}$ so energies will be same for

He & $H_{2}$ at same temperature.

Question 5.

The temperature and pressure at which ice, liquid water and water vapour can exist together are

0 $^{\circ}$ C, 1atm
2 $^{\circ}$ C, 4.7atm
0 $^{\circ}$ C, 4.7mm
2 $^{\circ}$ C, 4.7mm

Discuss Question

Answer: Option C. -> 0

^{\circ}

C, 4.7mm
:
C

All the three phases of water can coexist at 0 $^{\circ}$ C & 4.7 mm pressure.

Question 6.

In which of the gases given below, the average speed of the molecule is the least at 1000K?

$C O_{2}$
$S O_{2}$
$O_{2}$
$C H_{4}$

Discuss Question

Answer: Option B. ->

S O_{2}

:
B

Speed is inversely proportional to molecular weight. Molecular weight of $S O_{2}$ is highest among the four. Hence its speed is least.

Question 7.

The compressibility factor of a gas is less than 1 at STP. Its molar volume Vm will be

Vm > 22.42
Vm < 22.42
Vm = 22.42
None

Discuss Question

Answer: Option B. -> Vm < 22.42
:
B

If Z<1 then molar volume is less than 22.4 L

Question 8.

$n_{1}$ and $n_{2}$ moles of two ideal gases (mol. wt. $M_{1}$ and $M_{2}$ ) respectively at temperature $T_{1}$ K and $T_{2}$ K are mixed. Assuming that no loss of energy, the temperature of mixture becomes -

$n_{1} T_{1} + n_{2} T_{2}$
$\frac{n_{1} T_{1} + n_{2} T_{2}}{T_{1} + T_{2}}$
$\frac{n_{1} T_{1} + n_{2} T_{2}}{n_{1} + n_{2}}$
$\frac{n_{1} \times T_{2}}{n_{1} \times n_{2}}$

Discuss Question

Answer: Option C. ->

\frac{n_{1} T_{1} + n_{2} T_{2}}{n_{1} + n_{2}}

:
C

Let the final temperature be T , then K $E_{1}$ + K $E_{m i x t u r e}$

$\frac{3}{2}$ $n_{1} R T_{1}$ + $\frac{3}{2}$ $n_{2} R T_{2}$ = $\frac{3}{2}$ ( $n_{1} + n_{2}$ ) RT

T = $\frac{n_{1} T_{1} + n_{2} T_{2}}{n_{1} + n_{2}}$

Question 9.

At what temperature, the volume of 'V' of a certain mass of a gas at $37^{o} C$ will be doubled, keeping the pressure constant?

$327^{o} C$
$347^{o} C$
$527^{o} C$
$54^{o} C$

Discuss Question

Answer: Option B. ->

347^{o} C

:
B

\frac{V_{1}}{T_{1}} = \frac{V_{2}}{T_{2}}

V_{1} = V, T_{1} = 37 + 273 = 310 k

V_{2} = 2 V, T_{2} = ?

\frac{V}{310} = \frac{2 V}{T_{2}}

T_{2} = 620 K = 347^{o} C

Question 10.

A cubical vessel has a side with 'I' cm lenth contained a gas at a pressure of 'p'. when the side of the vessel is made $\frac{1}{2}$ cm, the pressure of gas becomes?