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Ideal gas equation and Related gas laws Questions in English

Class 11 Chemistry · States of Matter · Ideal gas equation and Related gas laws

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51
EasyMCQ
The equation for Boyle's law is:
A
$\frac{dP}{P} = - \frac{dV}{V}$
B
$\frac{dP}{P} = + \frac{dV}{V}$
C
$\frac{d^2P}{P} = - \frac{dV}{dT}$
D
$\frac{d^2P}{P} = + \frac{d^2V}{dT}$

Solution

(A) Boyle's law states that for a fixed amount of an ideal gas at constant temperature,$PV = k$ (where $k$ is a constant).
Taking the derivative of both sides with respect to the variables:
$d(PV) = d(k)$
Using the product rule: $P dV + V dP = 0$
Rearranging the terms: $V dP = -P dV$
Dividing both sides by $PV$: $\frac{dP}{P} = - \frac{dV}{V}$.
52
EasyMCQ
If $P$,$V$,$M$,$T$ and $R$ are pressure,volume,molar mass,temperature and gas constant respectively,then for an ideal gas,the density is given by
A
$\frac{RT}{PM}$
B
$\frac{P}{RT}$
C
$\frac{M}{V}$
D
$\frac{PM}{RT}$

Solution

(D) The ideal gas equation is given by $PV = nRT$.
Since the number of moles $n = \frac{m}{M}$,where $m$ is the mass and $M$ is the molar mass,we can write $PV = \frac{m}{M}RT$.
Rearranging the terms to solve for density $(d = \frac{m}{V})$,we get $d = \frac{m}{V} = \frac{PM}{RT}$.
Thus,the correct option is $D$.
53
EasyMCQ
An ideal gas will have maximum density when
A
$P = 0.5 \ atm, \ T = 600 \ K$
B
$P = 2 \ atm, \ T = 150 \ K$
C
$P = 1 \ atm, \ T = 300 \ K$
D
$P = 1.0 \ atm, \ T = 500 \ K$

Solution

(B) The density $(d)$ of an ideal gas is given by the formula $d = \frac{PM}{RT}$,where $P$ is pressure,$M$ is molar mass,$R$ is the gas constant,and $T$ is temperature.
Since $M$ and $R$ are constant,$d \propto \frac{P}{T}$.
Calculating the ratio $\frac{P}{T}$ for each option:
$A$: $\frac{0.5}{600} \approx 0.00083$
$B$: $\frac{2}{150} \approx 0.0133$
$C$: $\frac{1}{300} \approx 0.0033$
$D$: $\frac{1}{500} = 0.002$
The ratio $\frac{P}{T}$ is maximum for option $B$.
54
EasyMCQ
The density of neon will be highest at
A
$S.T.P.$
B
${0\,^oC}, 2\,atm$
C
${273\,^oC}, 1\,atm$
D
${273\,^oC}, 2\,atm$

Solution

(B) The density $(d)$ of an ideal gas is given by the formula $d = \frac{PM}{RT}$,where $P$ is pressure,$M$ is molar mass,$R$ is the gas constant,and $T$ is temperature in Kelvin.
Since $M$ and $R$ are constants,$d \propto \frac{P}{T}$.
For option $A$ $(S.T.P.)$: $P = 1\,atm$,$T = 273\,K$,so $d \propto \frac{1}{273} \approx 0.0036$.
For option $B$: $P = 2\,atm$,$T = 273\,K$,so $d \propto \frac{2}{273} \approx 0.0073$.
For option $C$: $P = 1\,atm$,$T = 546\,K$,so $d \propto \frac{1}{546} \approx 0.0018$.
For option $D$: $P = 2\,atm$,$T = 546\,K$,so $d \propto \frac{2}{546} \approx 0.0036$.
Comparing the values,the density is highest at ${0\,^oC}$ and $2\,atm$.
55
EasyMCQ
The density of a gas $A$ is three times that of a gas $B$. If the molecular mass of $A$ is $M$,the molecular mass of $B$ is:
A
$3 \, M$
B
$\sqrt{3} \, M$
C
$M / 3$
D
$M / \sqrt{3}$

Solution

(C) According to the ideal gas equation,$PV = nRT = (\frac{m}{M})RT$.
Rearranging for density $(d = \frac{m}{V})$,we get $d = \frac{PM}{RT}$.
Since $P$,$R$,and $T$ are constant,$d \propto M$.
Therefore,$\frac{d_A}{d_B} = \frac{M_A}{M_B}$.
Given $d_A = 3 \, d_B$ and $M_A = M$,we have $\frac{3 \, d_B}{d_B} = \frac{M}{M_B}$.
Solving for $M_B$,we get $M_B = \frac{M}{3}$.
56
MediumMCQ
The root mean square velocity of an ideal gas in a closed container of fixed volume is increased from $5 \times 10^4 \ cm \ s^{-1}$ to $10 \times 10^4 \ cm \ s^{-1}$. Which of the following statements correctly explains how the change is accomplished?
A
By heating the gas,the temperature is doubled
B
By heating the gas,the pressure is quadrupled (i.e.,made four times)
C
By heating the gas,the temperature is quadrupled
D
By heating the gas,the pressure is doubled

Solution

(B) The root mean square velocity $(U_{rms})$ is given by the formula $U_{rms} = \sqrt{\frac{3RT}{M}}$.
Since $U_{rms} \propto \sqrt{T}$,we have $\frac{U_1}{U_2} = \sqrt{\frac{T_1}{T_2}}$.
Given $U_1 = 5 \times 10^4 \ cm \ s^{-1}$ and $U_2 = 10 \times 10^4 \ cm \ s^{-1}$,then $\frac{U_1}{U_2} = \frac{1}{2}$.
Squaring both sides,$\frac{T_1}{T_2} = (\frac{1}{2})^2 = \frac{1}{4}$,which means $T_2 = 4T_1$.
For an ideal gas in a fixed volume,$P \propto T$ (Gay-Lussac's Law). Since the temperature is quadrupled,the pressure also becomes four times the initial value.
57
EasyMCQ
The compressibility factor of a gas is defined as $Z = PV/RT$. The compressibility factor of an ideal gas is:
A
$0$
B
Infinity
C
$1$
D
$-1$

Solution

(C) The compressibility factor $Z$ is defined as $Z = \frac{PV}{RT}$.
For an ideal gas,the ideal gas equation is $PV = nRT$. For $1 \text{ mole}$ of gas,$PV = RT$.
Substituting this into the expression for $Z$,we get $Z = \frac{RT}{RT} = 1$.
Therefore,the compressibility factor of an ideal gas is $1$.
58
EasyMCQ
The compressibility factor for an ideal gas is
A
$1.5$
B
$1$
C
$2$
D
$\alpha$

Solution

(B) The compressibility factor $Z$ is defined as $Z = \frac{PV}{nRT}$.
For an ideal gas,the equation of state is $PV = nRT$.
Substituting this into the expression for $Z$,we get $Z = \frac{nRT}{nRT} = 1$.
Therefore,the compressibility factor for an ideal gas is $1$.
59
DifficultMCQ
When an ideal gas undergoes unrestrained expansion,no cooling occurs because the molecules
A
Are above the inversion temperature
B
Exert no attractive force on each other
C
Do work equal to loss in kinetic energy
D
Collide without loss of energy

Solution

(B) In an ideal gas,there are no intermolecular forces of attraction between the particles.
During unrestrained expansion (expansion against vacuum),no work is done by the gas $(w = 0)$.
Since there are no attractive forces to overcome,no internal energy is consumed to separate the molecules,and therefore,the temperature of the ideal gas remains constant.
60
EasyMCQ
The temperature at which real gases obey the ideal gas laws over a wide range of pressure is called:
A
Critical temperature
B
Boyle temperature
C
Inversion temperature
D
Reduced temperature

Solution

(B) The temperature at which a real gas behaves like an ideal gas over an appreciable range of pressure is known as the $Boyle$ temperature or $Boyle$ point.
At this temperature,the compressibility factor $Z$ remains close to $1$ for a wide range of pressure.
61
MediumMCQ
The molecular weights of $O_2$ and $SO_2$ are $32$ and $64$ respectively. If $1 \, L$ of $O_2$ at $15 \, ^\circ C$ and $750 \, mm$ pressure contains '$N$' molecules,the number of molecules in $2 \, L$ of $SO_2$ under the same conditions of temperature and pressure will be
A
$N/2$
B
$N$
C
$2N$
D
$4N$

Solution

(C) According to Avogadro's Law,at the same temperature and pressure,equal volumes of all gases contain an equal number of molecules.
Given that $1 \, L$ of $O_2$ contains $N$ molecules at a specific temperature and pressure.
Therefore,$1 \, L$ of $SO_2$ will also contain $N$ molecules under the same conditions.
Consequently,$2 \, L$ of $SO_2$ will contain $2 \times N = 2N$ molecules.
62
MediumMCQ
In an experiment during the analysis of a carbon compound,$145 \ L$ of $H_2$ was collected at $760 \ mm \ Hg$ pressure and $27 \ ^oC$ temperature. The mass of $H_2$ is nearly $....... \ g$.
A
$10$
B
$12$
C
$24$
D
$6$

Solution

(B) Using the ideal gas equation,$PV = nRT$.
Given: $P = 760 \ mm \ Hg = 1 \ atm$,$V = 145 \ L$,$T = 27 \ ^oC = 300 \ K$,and $R = 0.082 \ L \ atm \ K^{-1} \ mol^{-1}$.
Calculating the number of moles $(n)$: $n = \frac{PV}{RT} = \frac{1 \times 145}{0.082 \times 300} \approx 5.89 \ mol \approx 6 \ mol$.
The molar mass of $H_2$ is $2 \ g/mol$.
Therefore,the mass of $H_2 = n \times \text{molar mass} = 6 \ mol \times 2 \ g/mol = 12 \ g$.
63
MediumMCQ
The volume of $1\, g$ each of methane $(CH_4)$,ethane $(C_2H_6)$,propane $(C_3H_8)$,and butane $(C_4H_{10})$ was measured at $350\, K$ and $1\, atm$. What is the volume of butane in $cm^{3}$?
A
$495$
B
$600$
C
$900$
D
$1700$

Solution

(A) Using the ideal gas equation,$PV = nRT$,where $n = \frac{m}{M}$.
For butane $(C_4H_{10})$,the molar mass $M = (4 \times 12) + (10 \times 1) = 58\, g/mol$.
Given $m = 1\, g$,$T = 350\, K$,$P = 1\, atm$,and $R = 0.0821\, L \cdot atm \cdot K^{-1} \cdot mol^{-1}$.
$V = \frac{nRT}{P} = \frac{m}{M} \times \frac{RT}{P} = \frac{1}{58} \times \frac{0.0821 \times 350}{1} \approx 0.4956\, L$.
Since $1\, L = 1000\, cm^3$,the volume is $0.4956 \times 1000 \approx 495.6\, cm^3$.
The closest option is $495\, cm^3$.
64
MediumMCQ
At what temperature in the Celsius scale,$V$ (volume) of a certain mass of gas at $27\,^oC$ will be doubled keeping the pressure constant?
A
$54$
B
$327$
C
$427$
D
$527$

Solution

(B) According to Charles's Law,at constant pressure,$\frac{V_1}{T_1} = \frac{V_2}{T_2}$.
Given: $V_1 = V$,$T_1 = 27 + 273 = 300\,K$,$V_2 = 2V$.
Substituting the values: $\frac{V}{300} = \frac{2V}{T_2}$.
$T_2 = 300 \times 2 = 600\,K$.
Converting to Celsius scale: $T_2 = 600 - 273 = 327\,^oC$.
65
DifficultMCQ
Pressure of a mixture of $4 \ g$ of $O_2$ and $2 \ g$ of $H_2$ confined in a bulb of $1 \ L$ at $0^{\circ}C$ is $..... \ atm$
A
$25.215$
B
$31.205$
C
$45.215$
D
$15.210$

Solution

(A) Number of moles of $O_2 = \frac{4 \ g}{32 \ g/mol} = 0.125 \ mol$.
Number of moles of $H_2 = \frac{2 \ g}{2 \ g/mol} = 1 \ mol$.
Total number of moles $(n)$ = $0.125 + 1 = 1.125 \ mol$.
Using the ideal gas equation $PV = nRT$,where $R = 0.0821 \ L \cdot atm \cdot K^{-1} \cdot mol^{-1}$ and $T = 273 \ K$:
$P = \frac{nRT}{V} = \frac{1.125 \times 0.0821 \times 273}{1} \approx 25.215 \ atm$.
66
MediumMCQ
If pressure becomes double at the same absolute temperature on $2 \ L$ $CO_2$,then the volume of $CO_2$ becomes ............ $L$.
A
$2$
B
$4$
C
$0.5$
D
$1$

Solution

(D) According to Boyle's Law,at constant temperature,$P_1V_1 = P_2V_2$.
Given: $V_1 = 2 \ L$,$P_2 = 2P_1$.
Substituting the values: $P_1 \times 2 \ L = (2P_1) \times V_2$.
$V_2 = \frac{P_1 \times 2 \ L}{2P_1} = 1 \ L$.
Therefore,the volume becomes $1 \ L$.
67
MediumMCQ
Volume of the air that will be expelled from a vessel of $300 \; cm^{3}$ when it is heated from $27 \; ^{\circ}C$ to $37 \; ^{\circ}C$ at the same pressure will be ........... $cm^{3}$
A
$310$
B
$290$
C
$10$
D
$37$

Solution

(C) According to Charles's Law,at constant pressure,$V \propto T$,so $\frac{V_1}{T_1} = \frac{V_2}{T_2}$.
Given: $V_1 = 300 \; cm^{3}$,$T_1 = 27 + 273 = 300 \; K$,$T_2 = 37 + 273 = 310 \; K$.
Calculating $V_2$: $V_2 = V_1 \times \frac{T_2}{T_1} = 300 \; cm^{3} \times \frac{310 \; K}{300 \; K} = 310 \; cm^{3}$.
The volume of air expelled is $\Delta V = V_2 - V_1 = 310 \; cm^{3} - 300 \; cm^{3} = 10 \; cm^{3}$.
68
MediumMCQ
$300 \ mL$ of a gas at $27 \ ^\circ C$ is cooled to $-3 \ ^\circ C$ at constant pressure. The final volume is ................ $mL$.
A
$540$
B
$135$
C
$270$
D
$350$

Solution

(C) According to Charles's Law,at constant pressure,$V \propto T$ or $\frac{V_1}{T_1} = \frac{V_2}{T_2}$.
Given: $V_1 = 300 \ mL$,$T_1 = 27 + 273 = 300 \ K$,$T_2 = -3 + 273 = 270 \ K$.
Substituting the values: $V_2 = \frac{T_2}{T_1} \times V_1 = \frac{270 \ K}{300 \ K} \times 300 \ mL = 270 \ mL$.
69
EasyMCQ
An ideal gas at constant temperature and pressure expands,then its
A
Internal energy remains same
B
Internal energy decreases
C
Internal energy increases
D
Entropy first increases and then decreases

Solution

(A) The internal energy $(U)$ of an ideal gas is a function of temperature only,i.e.,$U = f(T)$.
Since the process occurs at constant temperature $(T)$,the change in internal energy $(\Delta U)$ is zero.
Therefore,the internal energy remains the same.
70
EasyMCQ
The value of the universal gas constant $R$ is:
A
$0.082 \ L \ atm \ K^{-1} \ mol^{-1}$
B
$0.987 \ cal \ mol^{-1} \ K^{-1}$
C
$8.3 \ J \ mol^{-1} \ K^{-1}$
D
$83 \ erg \ mol^{-1} \ K^{-1}$

Solution

(A) The universal gas constant $R$ has different values depending on the units used.
For pressure in $atm$ and volume in $L$,$R = 0.0821 \ L \ atm \ K^{-1} \ mol^{-1}$.
In $SI$ units,where pressure is in $Pa$ $(N/m^2)$ and volume is in $m^3$,$R = 8.314 \ J \ K^{-1} \ mol^{-1}$.
Comparing the given options,option $A$ represents the correct value in $L \ atm \ K^{-1} \ mol^{-1}$.
71
MediumMCQ
An ideal gas expands against a constant external pressure of $3 \ atm$ from $4 \ dm^3$ to $6 \ dm^3$. The work done during this process is ..... $J$.
A
$-608$
B
$+304$
C
$-304$
D
$-6$
72
EasyMCQ
For an ideal gas,the value of ${\left( {\frac{{dU}}{{dV}}} \right)_T}$ is ...... .
A
Positive
B
Zero
C
Negative
D
Variable

Solution

(B) For an ideal gas,the internal energy $(U)$ is a function of temperature $(T)$ only.
It does not depend on the volume $(V)$ of the gas.
Therefore,the change in internal energy with respect to volume at constant temperature is zero,i.e.,${\left( {\frac{{dU}}{{dV}}} \right)_T = 0}$.
73
MediumMCQ
$100 \, mL$ of $O_2$ and $H_2$ are kept at the same temperature and pressure. Which of the following is true regarding the number of molecules?
A
$N_{O_2} > N_{H_2}$
B
$N_{O_2} < N_{H_2}$
C
$N_{O_2} = N_{H_2}$
D
$N_{O_2} + N_{H_2} = 0$

Solution

(C) According to Avogadro's Law,equal volumes of all gases at the same temperature and pressure contain an equal number of molecules.
Since the volume,temperature,and pressure are the same for both $O_2$ and $H_2$,the number of molecules will be equal.
74
DifficultMCQ
If $500 \ cm^3$ of hydrogen gas is at a pressure of $760 \ mm$ and a temperature of $300 \ K$,what is the number of moles?
A
$20.3 \times 10^{-2}$
B
$2.03 \times 10^{-2}$
C
$203 \times 10^{-2}$
D
None

Solution

(B) Using the ideal gas equation: $PV = nRT$
Given:
$P = 760 \ mm \ Hg = 1 \ atm$
$V = 500 \ cm^3 = 0.5 \ L$
$T = 300 \ K$
$R = 0.0821 \ L \ atm \ K^{-1} \ mol^{-1}$
Substituting the values:
$1 \ atm \times 0.5 \ L = n \times 0.0821 \ L \ atm \ K^{-1} \ mol^{-1} \times 300 \ K$
$n = \frac{0.5}{0.0821 \times 300}$
$n = \frac{0.5}{24.63} \approx 0.0203 \ mol$
$n = 2.03 \times 10^{-2} \ mol$
75
EasyMCQ
The density of a gas is equal to ...... ($P =$ pressure,$V =$ volume,$T =$ temperature,$R =$ gas constant,$n =$ number of moles,and $M_w =$ molecular weight):
A
$nP$
B
$\frac{P M_w}{RT}$
C
$\frac{P}{RT}$
D
$\frac{M_w}{V}$

Solution

(B) From the ideal gas equation,$PV = nRT$.
Since $n = \frac{m}{M_w}$ (where $m$ is mass and $M_w$ is molecular weight),we can write $PV = \frac{m}{M_w} RT$.
Rearranging the equation,we get $P M_w = \frac{m}{V} RT$.
Since density $d = \frac{m}{V}$,the equation becomes $P M_w = dRT$.
Therefore,$d = \frac{P M_w}{RT}$.
76
MediumMCQ
The graph of pressure $(P)$ versus density $(d)$ is shown for an ideal gas at two temperatures $T_1$ and $T_2$. Which of the following is correct?
Question diagram
A
$T_1 > T_2$
B
$T_1 = T_2$
C
$T_1 < T_2$
D
None of the above

Solution

(A) The ideal gas equation is $PV = nRT$.
Since $n = \frac{m}{M}$,we have $PV = \frac{m}{M}RT$.
Rearranging for pressure,$P = \frac{m}{V} \cdot \frac{RT}{M}$.
Since density $d = \frac{m}{V}$,the equation becomes $P = d \cdot \frac{RT}{M}$.
Comparing this with the equation of a straight line $y = mx$,where $y = P$ and $x = d$,the slope is $m = \frac{RT}{M}$.
Since $R$ and $M$ are constants,the slope is directly proportional to temperature $T$.
From the graph,the slope of the line for $T_1$ is greater than the slope of the line for $T_2$.
Therefore,$T_1 > T_2$.
77
DifficultMCQ
$A$ bulb of $1 \, L$ capacity contains $5 \, g$ of ethane. If the pressure increases to $10 \, atm$,what will be the temperature in $^oC$ at which the bulb will burst?
A
$387.30$
B
$745.81$
C
$475.81$
D
$457.81$

Solution

(D) Given: $wt = 5 \, g$,$V = 1 \, L$,$P = 10 \, atm$,Molar mass of ethane $(C_2H_6)$ $M_w = 30 \, g/mol$.
Using the ideal gas equation: $PV = nRT = \frac{wt}{M_w} RT$.
Substituting the values: $10 \times 1 = \frac{5}{30} \times 0.0821 \times T$.
$T = \frac{10 \times 30}{5 \times 0.0821} = \frac{300}{0.4105} \approx 730.81 \, K$.
Converting to Celsius: $T(^oC) = T(K) - 273.15 = 730.81 - 273.15 = 457.66 \, ^oC$.
Rounding to the nearest provided option,the correct value is $457.81 \, ^oC$.
78
MediumMCQ
$A$ gas occupies $0.418 \ L$ at $27 \ ^\circ C$ and $740 \ mm \ Hg$ pressure. What will be its volume at $STP$ in $L$?
A
$2.35$
B
$1.76$
C
$0.37$
D
$3.44$

Solution

(C) Given: $T_1 = 27 + 273 = 300 \ K$,$V_1 = 0.418 \ L$,$P_1 = \frac{740}{760} \ atm$.
At $STP$: $T_2 = 273 \ K$,$P_2 = 1 \ atm$,$V_2 = ?$.
Using the combined gas law: $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$.
Substituting the values: $\frac{(\frac{740}{760}) \times 0.418}{300} = \frac{1 \times V_2}{273}$.
$V_2 = \frac{740 \times 0.418 \times 273}{760 \times 300} \approx 0.37 \ L$.
79
EasyMCQ
The value of the gas constant $R$ is $8.314 \ X$. Here,$X$ represents ......
A
$J \ K^{-1} \ mol^{-1}$
B
$cal \ K^{-1} \ mol^{-1}$
C
$L \ atm \ K^{-1} \ mol^{-1}$
D
None of the above

Solution

(A) The universal gas constant $R$ has different values depending on the units used for pressure,volume,and temperature.
For the $SI$ unit system,where pressure is in $Pa$ $(N \ m^{-2})$,volume is in $m^3$,and temperature is in $K$,the value of $R$ is $8.314 \ J \ K^{-1} \ mol^{-1}$.
Since $1 \ J = 1 \ Pa \ m^3$,the unit $J \ K^{-1} \ mol^{-1}$ is the correct $SI$ unit for $R = 8.314$.
80
MediumMCQ
An ideal gas with a molar mass of $40 \ g \ mol^{-1}$ has a mass of $120 \ g$. It occupies a volume of $20 \ L$ at a temperature of $400 \ K$. Using $R = 0.0821 \ L \ atm \ K^{-1} \ mol^{-1}$,the pressure of the gas is ........ $atm$.
A
$4.90$
B
$4.92$
C
$5.02$
D
$4.96$

Solution

(B) Given:
Mass of gas $(w)$ = $120 \ g$
Molar mass $(M)$ = $40 \ g \ mol^{-1}$
Volume $(V)$ = $20 \ L$
Temperature $(T)$ = $400 \ K$
Gas constant $(R)$ = $0.0821 \ L \ atm \ K^{-1} \ mol^{-1}$
Step $1$: Calculate the number of moles $(n)$:
$n = \frac{w}{M} = \frac{120 \ g}{40 \ g \ mol^{-1}} = 3 \ mol$
Step $2$: Use the ideal gas equation $PV = nRT$ to find pressure $(P)$:
$P = \frac{nRT}{V}$
$P = \frac{3 \ mol \times 0.0821 \ L \ atm \ K^{-1} \ mol^{-1} \times 400 \ K}{20 \ L}$
$P = \frac{3 \times 0.0821 \times 400}{20}$
$P = 3 \times 0.0821 \times 20$
$P = 60 \times 0.0821 = 4.926 \ atm$
Rounding to the nearest provided option,the pressure is $4.92 \ atm$.
81
MediumMCQ
What is the volume in $litre$ occupied by $7 \, g$ of $N_2$ gas at $27 \, ^oC$ temperature and $750 \, mm \, Hg$ pressure?
A
$6.3$
B
$7.3$
C
$6.8$
D
$5.3$

Solution

(A) Given: $w = 7 \, g$,$P = \frac{750}{760} \, atm$,$M_w = 28 \, g/mol$,$T = 27 + 273 = 300 \, K$.
Using the ideal gas equation: $PV = nRT = \frac{w}{M_w} RT$.
Substituting the values: $\frac{750}{760} \times V = \frac{7}{28} \times 0.0821 \times 300$.
$V = \frac{0.25 \times 0.0821 \times 300 \times 760}{750} \approx 6.29 \, L$.
Thus,the volume is approximately $6.3 \, L$.
82
EasyMCQ
What is the density of $CO_2$ at $100\,^oC$ and $800\,mm\,Hg$ pressure in $g/L$?
A
$0.58$
B
$1.51$
C
$2.38$
D
$3.18$

Solution

(B) The density $(d)$ of a gas is given by the ideal gas equation: $d = \frac{PM_w}{RT}$
Given:
Pressure $(P)$ = $\frac{800}{760} \, atm$
Molar mass $(M_w)$ of $CO_2$ = $44 \, g/mol$
Temperature $(T)$ = $100 + 273 = 373 \, K$
Gas constant $(R)$ = $0.0821 \, L \cdot atm \cdot K^{-1} \cdot mol^{-1}$
Substituting the values:
$d = \frac{(\frac{800}{760}) \times 44}{0.0821 \times 373}$
$d \approx 1.5124 \, g/L$
83
MediumMCQ
$A$ container is divided into two equal parts $A$ and $B$ containing $H_2$ and $O_2$ respectively,each at $1 \ atm$ pressure. If the wall separating the two sections is removed,what happens to the pressure?
A
Pressure remains unchanged in both $A$ and $B$.
B
Pressure increases in $A$ and decreases in $B$.
C
Pressure decreases in $A$ and increases in $B$.
D
Pressure increases in both $A$ and $B$.

Solution

(A) Initially,both parts $A$ and $B$ have equal volumes $(V)$ and equal pressures $(P = 1 \ atm)$.
When the partition is removed,the total volume becomes $2V$.
According to Boyle's Law,$P_1V_1 = P_2V_2$.
For the total system,the final pressure $P_f$ is calculated as: $P_f = \frac{P_A V + P_B V}{2V} = \frac{1 \times V + 1 \times V}{2V} = 1 \ atm$.
Since the gases mix and occupy the total volume,the partial pressure of each gas decreases to $0.5 \ atm$,but the total pressure of the mixture remains $1 \ atm$ throughout the container.
84
EasyMCQ
The density of nitrogen monoxide $(NO)$ at $S.T.P.$ is ......... $g \ L^{-1}$.
A
$3$
B
$30$
C
$1.34$
D
$2.68$

Solution

(C) At $S.T.P.$ (Standard Temperature and Pressure),the molar volume of an ideal gas is $22.4 \ L \ mol^{-1}$.
The molar mass of nitrogen monoxide $(NO)$ is $14 + 16 = 30 \ g \ mol^{-1}$.
The density $(d)$ is calculated using the formula: $d = \frac{\text{Molar Mass}}{\text{Molar Volume}}$.
$d = \frac{30 \ g \ mol^{-1}}{22.4 \ L \ mol^{-1}} \approx 1.34 \ g \ L^{-1}$.
85
EasyMCQ
Which of the following statements is incorrect?
A
The pressure exerted by a fixed amount of gas is independent of temperature.
B
Molecules of different gases possess the same kinetic energy at a given temperature.
C
The gas equation is not valid at high pressure and low temperature.
D
The gas constant per molecule is known as the Boltzmann constant.

Solution

(A) According to the ideal gas law,$PV = nRT$,which implies $P = \frac{nRT}{V}$.
Thus,the pressure $P$ is directly proportional to temperature $T$ $(P \propto T)$.
Therefore,the statement that pressure is independent of temperature is incorrect.
Option $B$ is correct because average kinetic energy of gas molecules is $KE = \frac{3}{2}RT$,which depends only on temperature.
Option $C$ is correct because real gases deviate from ideal behavior at high pressure and low temperature.
Option $D$ is correct because the Boltzmann constant $k_B = \frac{R}{N_A}$ represents the gas constant per molecule.
86
MediumMCQ
At the same temperature,gas $A$ is taken in a $0.5 \, dm^3$ flask and gas $B$ is taken in a $1 \, dm^3$ flask. If the density of $A$ is $3.0 \, g \, dm^{-3}$ and that of $B$ is $1.5 \, g \, dm^{-3}$,and the molar mass of $A$ is $1/2$ of $B$,what is the ratio of the pressures exerted by the gases?
A
$\frac{P_A}{P_B} = 2$
B
$\frac{P_A}{P_B} = 1$
C
$\frac{P_A}{P_B} = 4$
D
$\frac{P_A}{P_B} = 3$

Solution

(C) The ideal gas equation is $PV = nRT$,where $n = \frac{m}{M}$.
Substituting $n$,we get $PV = \frac{m}{M} RT$.
Since density $d = \frac{m}{V}$,we can write $P = \frac{dRT}{M}$.
For gas $A$: $P_A = \frac{d_A RT}{M_A}$.
For gas $B$: $P_B = \frac{d_B RT}{M_B}$.
The ratio is $\frac{P_A}{P_B} = \frac{d_A}{d_B} \times \frac{M_B}{M_A}$.
Given $d_A = 3.0 \, g \, dm^{-3}$,$d_B = 1.5 \, g \, dm^{-3}$,and $M_A = \frac{1}{2} M_B$ (or $\frac{M_B}{M_A} = 2$).
Substituting these values: $\frac{P_A}{P_B} = \frac{3.0}{1.5} \times 2 = 2 \times 2 = 4$.
87
EasyMCQ
In the equation $PV = nRT$,which of the following is not equal to the numerical value of $R$?
A
$8.31 \times 10^7 \, \text{ergs} \, K^{-1} \, mol^{-1}$
B
$8.31 \times 10^7 \, \text{dynes} \, cm \, K^{-1} \, mol^{-1}$
C
$8.31 \, J \, K^{-1} \, mol^{-1}$
D
$8.31 \, L \, atm \, K^{-1} \, mol^{-1}$

Solution

(D) The universal gas constant $R$ has different values depending on the units used:
$1$. In $SI$ units,$R = 8.314 \, J \, K^{-1} \, mol^{-1}$.
$2$. In $CGS$ units,$1 \, J = 10^7 \, \text{ergs}$,so $R = 8.314 \times 10^7 \, \text{ergs} \, K^{-1} \, mol^{-1}$.
$3$. Since $1 \, J = 1 \, N \cdot m$ and $1 \, N = 10^5 \, \text{dynes}$,$1 \, J = 10^5 \, \text{dynes} \times 10^2 \, cm = 10^7 \, \text{dynes} \cdot cm$. Thus,$8.314 \times 10^7 \, \text{dynes} \cdot cm \, K^{-1} \, mol^{-1}$ is also correct.
$4$. In $L \cdot atm$ units,$R = 0.0821 \, L \cdot atm \, K^{-1} \, mol^{-1}$.
Therefore,the value $8.31 \, L \cdot atm \, K^{-1} \, mol^{-1}$ is incorrect.
88
DifficultMCQ
If $500 \ mL$ of gas $A$ at $1000 \ torr$ and $1000 \ mL$ of gas $B$ at $800 \ torr$ are taken in a $2 \ L$ container,the final pressure is .......... $torr$.
A
$100$
B
$650$
C
$1800$
D
$2400$

Solution

(B) Using Boyle's Law,$P_1V_1 = P_2V_2$ at constant temperature.
For gas $A$: $1000 \ torr \times 500 \ mL = P_A \times 2000 \ mL$. So,$P_A = (1000 \times 500) / 2000 = 250 \ torr$.
For gas $B$: $800 \ torr \times 1000 \ mL = P_B \times 2000 \ mL$. So,$P_B = (800 \times 1000) / 2000 = 400 \ torr$.
According to Dalton's Law of partial pressures,the total pressure $P_{total} = P_A + P_B$.
$P_{total} = 250 \ torr + 400 \ torr = 650 \ torr$.
89
EasyMCQ
In the gas equation $PV = nRT$,the universal gas constant $R$ depends on:
A
Nature of the gas
B
Pressure of the gas
C
Temperature of the gas
D
Units of measurement

Solution

(D) The ideal gas equation is given by $PV = nRT$,where $R$ is the universal gas constant.
$R$ is a universal constant,meaning its value does not depend on the nature,pressure,or temperature of the gas.
However,the numerical value of $R$ depends on the units used for pressure $(P)$,volume $(V)$,and temperature $(T)$.
For example,$R = 0.0821 \ L \ atm \ K^{-1} \ mol^{-1}$ when using liters and atmospheres,but $R = 8.314 \ J \ K^{-1} \ mol^{-1}$ in $SI$ units.
90
EasyMCQ
The density of a gas at $-23 \ ^oC$ temperature and $780 \ \text{torr}$ pressure is $1.40 \ g/L$. Identify the gas.
A
$CO_2$
B
$SO_2$
C
$Cl_2$
D
$N_2$

Solution

(D) Using the ideal gas equation in terms of density: $d = \frac{PM_w}{RT}$
Given: $P = \frac{780}{760} \ atm$,$T = -23 + 273 = 250 \ K$,$d = 1.40 \ g/L$,$R = 0.0821 \ L \cdot atm \cdot K^{-1} \cdot mol^{-1}$
Substituting the values: $1.40 = \frac{(\frac{780}{760}) \times M_w}{0.0821 \times 250}$
$M_w = \frac{1.40 \times 0.0821 \times 250 \times 760}{780} \approx 28 \ g/mol$
The molar mass of $N_2$ is $28 \ g/mol$. Therefore,the gas is $N_2$.
91
EasyMCQ
$A$ gas occupies $10 \ L$ at $STP$. Which of the following conditions will result in the same volume?
A
$273 \ K$ and $2 \ atm$
B
$273 \ ^oC$ and $2 \ atm$
C
$546 \ ^oC$ and $0.5 \ atm$
D
$0 \ ^oC$ and $0 \ atm$

Solution

(B) According to the ideal gas law,$PV = nRT$. Since the amount of gas $(n)$ is constant,the relationship is $\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$.
At $STP$,$P_1 = 1 \ atm$,$T_1 = 273 \ K$,and $V_1 = 10 \ L$.
We want $V_2 = 10 \ L$,so the condition $\frac{P_1}{T_1} = \frac{P_2}{T_2}$ must be satisfied.
For option $A$: $\frac{1}{273} \neq \frac{2}{273}$.
For option $B$: $T_2 = 273 + 273 = 546 \ K$. $\frac{P_2}{T_2} = \frac{2}{546} = \frac{1}{273}$. This matches the initial condition.
Therefore,option $B$ is correct.
92
MediumMCQ
$A$ $3.7 \ g$ sample of a gas occupies the same volume at $25 \ ^\circ C$ as $0.184 \ g$ of $H_2$ gas at $17 \ ^\circ C$ at the same pressure. The molecular weight of the gas is:
A
$35.962$
B
$55.152$
C
$41.326$
D
$39.458$

Solution

(C) Given: For the unknown gas,$w_1 = 3.7 \ g$,$T_1 = 25 + 273 = 298 \ K$.
For $H_2$ gas,$w_2 = 0.184 \ g$,$T_2 = 17 + 273 = 290 \ K$,$M_2 = 2 \ g/mol$.
Since pressure and volume are the same,we use the ideal gas law $PV = nRT = (w/M)RT$.
Thus,$(w_1/M_1)T_1 = (w_2/M_2)T_2$.
Substituting the values: $(3.7/M_1) \times 298 = (0.184/2) \times 290$.
$M_1 = (3.7 \times 298 \times 2) / (0.184 \times 290) = 2205.2 / 53.36 \approx 41.326 \ g/mol$.
93
MediumMCQ
$A$ gas occupies $600 \ mL$ at $27 \ ^\circ C$ and $730 \ mm$ pressure. What will be its volume at $STP$ in $litres$?
A
$1.01$
B
$0.52$
C
$0.25$
D
$2.25$

Solution

(B) Using the combined gas law: $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$
Given:
$P_1 = \frac{730}{760} \ atm$,$V_1 = 600 \ mL = 0.6 \ L$,$T_1 = 27 + 273 = 300 \ K$
At $STP$:
$P_2 = 1 \ atm$,$T_2 = 273 \ K$
Substituting the values:
$\frac{(\frac{730}{760}) \times 0.6}{300} = \frac{1 \times V_2}{273}$
$V_2 = \frac{730 \times 0.6 \times 273}{760 \times 300} \approx 0.524 \ L$
94
EasyMCQ
At $25 \, ^\circ C$,the density of oxygen gas is $1.458 \, mg/L$ at $1 \, atm$ pressure. What will be the pressure of oxygen gas if the density is doubled?
A
$0.5 \, atm$
B
$2 \, atm$
C
$4 \, atm$
D
None of these

Solution

(B) According to the ideal gas equation,$PV = nRT = (m/M)RT$,where $P$ is pressure,$V$ is volume,$m$ is mass,$M$ is molar mass,$R$ is the gas constant,and $T$ is temperature.
Rearranging for density $(d = m/V)$,we get $P = (dRT)/M$.
Since $R$,$T$,and $M$ are constant for a given gas at a constant temperature,the pressure $P$ is directly proportional to the density $d$ $(P \propto d)$.
Given that the initial density $d_1 = 1.458 \, mg/L$ at $P_1 = 1 \, atm$,if the new density $d_2 = 2 \times d_1$,then the new pressure $P_2$ will be $2 \times P_1$.
Therefore,$P_2 = 2 \times 1 \, atm = 2 \, atm$.
95
EasyMCQ
At constant pressure,the volume of a gas is $300 \ mL$. If the temperature is changed from $27 \ ^oC$ to $-3 \ ^oC$,what will be the final volume in $mL$?
A
$540$
B
$135$
C
$270$
D
$350$

Solution

(C) According to Charles's Law,at constant pressure,$V \propto T$ or $\frac{V_1}{T_1} = \frac{V_2}{T_2}$.
Given: $V_1 = 300 \ mL$,$T_1 = 27 \ ^oC = 27 + 273 = 300 \ K$,$T_2 = -3 \ ^oC = -3 + 273 = 270 \ K$.
Substituting the values: $\frac{300}{300} = \frac{V_2}{270}$.
Therefore,$V_2 = 270 \ mL$.
96
MediumMCQ
The volume of $1 \ g$ of methane $(CH_4)$,ethane $(C_2H_6)$,propane $(C_3H_8)$,and butane $(C_4H_{10})$ is measured at $350 \ K$ and $1 \ atm$ pressure. What will be the volume of butane in $cm^3$?
A
$495$
B
$600$
C
$900$
D
$1700$

Solution

(A) Using the ideal gas equation: $PV = nRT = \frac{w}{M_w} RT$
Rearranging for volume: $V = \frac{wRT}{P M_w}$
Given values: $w = 1 \ g$,$R = 0.0821 \ L \ atm \ K^{-1} \ mol^{-1}$,$T = 350 \ K$,$P = 1 \ atm$,and molar mass of butane $(C_4H_{10}) = 4 \times 12 + 10 \times 1 = 58 \ g/mol$.
Substituting the values: $V = \frac{1 \times 0.0821 \times 350}{1 \times 58} \approx 0.495 \ L$
Since $1 \ L = 1000 \ cm^3$,$V = 0.495 \times 1000 = 495 \ cm^3$.
97
EasyMCQ
At constant pressure,by what percentage must the temperature in Kelvin be increased to increase the volume by $10\%$?
A
$10$
B
$20$
C
$5$
D
$50$

Solution

(A) According to Charles's Law,at constant pressure,$V \propto T$,which means $\frac{V_1}{T_1} = \frac{V_2}{T_2}$.
Given that the volume increases by $10\%$,$V_2 = V_1 + 0.10V_1 = 1.10V_1$.
Substituting this into the equation: $\frac{V_1}{T_1} = \frac{1.10V_1}{T_2}$.
Solving for $T_2$: $T_2 = 1.10T_1$.
The percentage increase in temperature is $\frac{T_2 - T_1}{T_1} \times 100 = \frac{1.10T_1 - T_1}{T_1} \times 100 = 0.10 \times 100 = 10\%$.

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