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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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351
Medium
If the volume of $N_2$ gas at $STP$ is $204.75 \, mL$,then calculate the volume of the gas at $1.5 \, bar$ pressure and $127 \, ^oC$ temperature.

Solution

(200 ML) Using the combined gas law: $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$
At $STP$,$T_1 = 273 \, K$ and $P_1 = 1 \, bar$.
Given $V_1 = 204.75 \, mL$.
For the final state: $T_2 = 127 + 273 = 400 \, K$ and $P_2 = 1.5 \, bar$.
Substituting the values: $\frac{1 \times 204.75}{273} = \frac{1.5 \times V_2}{400}$.
Solving for $V_2$: $V_2 = \frac{204.75 \times 400}{273 \times 1.5} = 200 \, mL$.
352
Medium
At $400\, K$ temperature,the volume and pressure of a gas are $200\, mL$ and $1.5\, bar$ respectively. Calculate the volume,weight (assuming the gas is $N_2$),and the number of molecules at $STP$. $[R = 8.31 \times 10^{-2}\, L\, bar\, K^{-1}\, mol^{-1}]$.

Solution

(N/A) $1$. Using the ideal gas law $PV = nRT$,calculate the number of moles $(n)$: $n = \frac{PV}{RT} = \frac{1.5 \times 0.2}{0.0831 \times 400} = 0.009025\, mol$.
$2$. At $STP$ $(273.15\, K, 1\, bar)$,the volume of $1\, mol$ of gas is $22.7\, L$. Thus,$V_{STP} = n \times 22.7 = 0.009025 \times 22.7 = 0.2048\, L = 204.8\, mL$.
$3$. Weight of $N_2$ $(M = 28\, g/mol)$: $w = n \times M = 0.009025 \times 28 = 0.2527\, g$.
$4$. Number of molecules: $N = n \times N_A = 0.009025 \times 6.022 \times 10^{23} = 5.435 \times 10^{21}$ molecules.
353
Medium
Derive the relation between density $(d)$ and molar mass $(M)$ for an ideal gas.

Solution

(N/A) According to the ideal gas equation,$pV = nRT$.
$\therefore \frac{p}{RT} = \frac{n}{V}$ (Eq.-$i$).
We know that the number of moles $(n) = \frac{\text{mass }(m)}{\text{molar mass }(M)}$ (Eq.-$ii$).
Substituting the value of $n$ from (Eq.-$ii$) into (Eq.-$i$):
$\frac{p}{RT} = \left(\frac{m}{V}\right) \frac{1}{M}$.
Since density $(d) = \frac{\text{mass }(m)}{\text{volume }(V)}$,we can substitute $d$ into the equation:
$\frac{p}{RT} = \frac{d}{M}$.
Rearranging the equation to solve for $d$ or $M$:
$d = \frac{pM}{RT}$ or $M = \frac{dRT}{p}$.
This shows that the molar mass $(M)$ is directly proportional to the density $(d)$ of the gas at constant pressure and temperature.
354
MediumMCQ
If the density of a gas at sea level is $1.5 \ mg \ L^{-1}$,find the density of that gas on Mount Abu,where the pressure is $0.5 \ bar$. (Assume pressure at sea level is $1.0 \ bar$ and use the formula $\frac{d_1}{d_2} = \frac{p_1}{p_2}$) (in $mg \ L^{-1}$)
A
$0.75$
B
$1.5$
C
$3.0$
D
$0.5$

Solution

(A) Given:
Density at sea level $(d_1)$ = $1.5 \ mg \ L^{-1}$
Pressure at sea level $(p_1)$ = $1.0 \ bar$
Pressure at Mount Abu $(p_2)$ = $0.5 \ bar$
Using the formula: $\frac{d_1}{d_2} = \frac{p_1}{p_2}$
$\frac{1.5}{d_2} = \frac{1.0}{0.5}$
$d_2 = \frac{1.5 \times 0.5}{1.0} = 0.75 \ mg \ L^{-1}$
Therefore,the density of the gas on Mount Abu is $0.75 \ mg \ L^{-1}$.
355
MediumMCQ
Find the pressure of neon gas having density $0.9 \ g \ L^{-1}$ at $350 \ K$ temperature. $(R = 8.34 \times 10^{-2} \ bar \ L \ K^{-1} \ mol^{-1})$ (in $bar$)
A
$1.458$
B
$1.309$
C
$1.250$
D
$1.100$

Solution

(B) The ideal gas equation is given by $PV = nRT$.
Since $n = \frac{m}{M}$,we have $PV = \frac{m}{M} RT$.
Rearranging for pressure $P$,we get $P = \frac{m}{V} \times \frac{RT}{M} = \frac{dRT}{M}$.
Here,density $d = 0.9 \ g \ L^{-1}$,$R = 8.34 \times 10^{-2} \ bar \ L \ K^{-1} \ mol^{-1}$,$T = 350 \ K$,and the molar mass of neon $M = 20.18 \ g \ mol^{-1}$.
Substituting the values: $P = \frac{0.9 \times 8.34 \times 10^{-2} \times 350}{20.18} \approx 1.309 \ bar$.
356
Difficult
At $27\,^oC$ temperature in a $2\, L$ closed vessel,$10\, g$ of $H_2$ and $22\, g$ of $CO_2$ gases are filled. Find the partial pressure of each gas and the total pressure of the mixture. (Use $R = 0.08314\, L \cdot bar \cdot K^{-1} \cdot mol^{-1}$ and formula $pV = nRT$)

Solution

(N/A) $1$. Calculate moles of each gas:
$n(H_2) = \frac{10\, g}{2\, g/mol} = 5\, mol$
$n(CO_2) = \frac{22\, g}{44\, g/mol} = 0.5\, mol$
$2$. Convert temperature to Kelvin:
$T = 27 + 273 = 300\, K$
$3$. Calculate partial pressures using $p = \frac{nRT}{V}$:
$p(H_2) = \frac{5 \times 0.08314 \times 300}{2} = 62.355\, bar$
$p(CO_2) = \frac{0.5 \times 0.08314 \times 300}{2} = 6.2355\, bar$
$4$. Calculate total pressure:
$P_{total} = p(H_2) + p(CO_2) = 62.355 + 6.2355 = 68.5905\, bar$
357
DifficultMCQ
At $27\,^oC$ temperature,$4\,mol$ $Cl_2$,$4\,mol$ $N_2$,and $2\,mol$ $O_2$ are filled in a $5\,L$ closed vessel. Find the total pressure of the gaseous mixture. $(R = 8.34 \times 10^{-2} \,bar \,L \,mol^{-1} \,K^{-1})$ (in $,bar$)
A
$49.88$
B
$24.94$
C
$12.47$
D
$99.76$

Solution

(A) The total number of moles of the gas mixture is $n_{total} = n_{Cl_2} + n_{N_2} + n_{O_2} = 4 + 4 + 2 = 10 \,mol$.
The temperature in Kelvin is $T = 27 + 273 = 300 \,K$.
The volume of the vessel is $V = 5 \,L$.
Using the ideal gas equation $PV = nRT$,the total pressure $P$ is given by $P = \frac{n_{total}RT}{V}$.
Substituting the values: $P = \frac{10 \,mol \times 8.34 \times 10^{-2} \,bar \,L \,mol^{-1} \,K^{-1} \times 300 \,K}{5 \,L}$.
$P = \frac{10 \times 0.0834 \times 300}{5} = \frac{250.2}{5} = 50.04 \,bar$.
Given the options,the closest value is $49.88 \,bar$.
358
Medium
At $298 \, K$ temperature,$4 \, g$ of $H_2$ gas is filled in a $500 \, mL$ vessel. Due to a small hole in the vessel,after some time,the pressure in the vessel becomes $50 \, bar$. Find the number of $H_2$ molecules that have escaped from the vessel? $(R = 8.314 \times 10^{-2} \, L \, bar \, mol^{-1} \, K^{-1})$

Solution

(A) $1$. Initial moles of $H_2$ $(n_1)$ = $\frac{\text{mass}}{\text{molar mass}} = \frac{4 \, g}{2 \, g/mol} = 2 \, mol$.
$2$. Final moles of $H_2$ $(n_2)$ remaining in the vessel can be calculated using the ideal gas equation $PV = nRT$:
$n_2 = \frac{PV}{RT} = \frac{50 \, bar \times 0.5 \, L}{8.314 \times 10^{-2} \, L \, bar \, mol^{-1} \, K^{-1} \times 298 \, K} \approx 1.0086 \, mol$.
$3$. Moles of $H_2$ escaped = $n_1 - n_2 = 2 - 1.0086 = 0.9914 \, mol$.
$4$. Number of molecules escaped = $\text{moles} \times N_A = 0.9914 \times 6.022 \times 10^{23} \approx 5.97 \times 10^{23}$ molecules.
359
Medium
At $25 \, ^\circ C$ temperature and $760 \, mm \, Hg$ pressure,the volume of a gas is $600 \, mL$. Calculate the pressure when the volume of this gas becomes $640 \, mL$ at $10 \, ^\circ C$ temperature. Use the ideal gas equation: $\frac{p_1 V_1}{T_1} = \frac{p_2 V_2}{T_2}$

Solution

(676.6 MM HG) Given:
$p_1 = 760 \, mm \, Hg$
$V_1 = 600 \, mL$
$T_1 = 25 + 273 = 298 \, K$
$V_2 = 640 \, mL$
$T_2 = 10 + 273 = 283 \, K$
Using the combined gas law: $\frac{p_1 V_1}{T_1} = \frac{p_2 V_2}{T_2}$
$p_2 = \frac{p_1 V_1 T_2}{T_1 V_2}$
$p_2 = \frac{760 \times 600 \times 283}{298 \times 640}$
$p_2 = \frac{129048000}{190720} \approx 676.6 \, mm \, Hg$
360
Medium
At $21\, ^oC$ temperature,the volume of $212\, g$ of $O_2$ gas is $34\, dm^3$. If the pressure of the gas becomes $1.24\, bar$,then how many grams of $O_2$ gas are left in the container? $(R = 0.083\, dm^3\, bar\, K^{-1}\, mol^{-1})$

Solution

(D) Step $1$: Calculate the initial pressure $(P_1)$ using the Ideal Gas Equation $PV = nRT$.
$n_1 = \frac{212\, g}{32\, g/mol} = 6.625\, mol$.
$T = 21 + 273.15 = 294.15\, K$.
$P_1 = \frac{n_1RT}{V} = \frac{6.625 \times 0.083 \times 294.15}{34} = 4.76\, bar$.
Step $2$: Calculate the new amount of gas $(n_2)$ at $P_2 = 1.24\, bar$ using $PV = nRT$ (assuming $V$ and $T$ are constant).
$n_2 = \frac{P_2V}{RT} = \frac{1.24 \times 34}{0.083 \times 294.15} = 1.727\, mol$.
Step $3$: Convert moles to mass.
$Mass = n_2 \times Molar\, mass = 1.727 \times 32 = 55.26\, g$.
(Note: The provided solution $156.74\, g$ appears to be incorrect based on the calculation; the correct remaining mass is $55.26\, g$).
361
EasyMCQ
At what temperature will the volume of a gas be halved if the initial temperature is $17^{\circ}C$ and the pressure remains constant (in $^{\circ}C$)?
A
$-128$
B
$8.5$
C
$34$
D
$17$

Solution

(A) According to Charles's Law,at constant pressure,$V \propto T$ (where $T$ is in Kelvin).
Initial temperature $T_1 = 17 + 273 = 290 \ K$.
Initial volume $V_1 = V$.
Final volume $V_2 = V/2$.
Using the relation $\frac{V_1}{T_1} = \frac{V_2}{T_2}$:
$\frac{V}{290} = \frac{V/2}{T_2}$
$T_2 = \frac{290}{2} = 145 \ K$.
Converting back to Celsius: $145 - 273 = -128^{\circ}C$.
362
MediumMCQ
$A$ gas occupies $10 \ L$ at $0 \ ^{\circ}C$ and $2 \ atm$ pressure. At what temperature will the pressure in the container be $2.5 \ atm$,assuming the volume remains constant (in $^{\circ}C$)?
A
$273$
B
$68.25$
C
$341.25$
D
$136.5$

Solution

(B) According to Gay-Lussac's Law,for a constant volume,$\frac{P_1}{T_1} = \frac{P_2}{T_2}$.
Given: $P_1 = 2 \ atm$,$T_1 = 0 \ ^{\circ}C = 273 \ K$,$P_2 = 2.5 \ atm$.
Substituting the values: $\frac{2}{273} = \frac{2.5}{T_2}$.
$T_2 = \frac{2.5 \times 273}{2} = 341.25 \ K$.
Converting to Celsius: $T(^{\circ}C) = 341.25 - 273 = 68.25 \ ^{\circ}C$.
363
MediumMCQ
Calculate the pressure of $HCl$ gas having a density of $8 \, kg \, m^{-3}$ at a temperature of $-40 \, ^oC$. (Given: $R = 8.314 \, J \, K^{-1} \, mol^{-1}$,Molar mass of $HCl = 36.5 \, g \, mol^{-1} = 0.0365 \, kg \, mol^{-1}$)
A
$4.24 \times 10^{5} \, Pa$
B
$5.24 \times 10^{5} \, Pa$
C
$3.24 \times 10^{5} \, Pa$
D
$6.24 \times 10^{5} \, Pa$

Solution

(A) The ideal gas equation is given by $PV = nRT$.
Since $n = \frac{m}{M}$ and density $d = \frac{m}{V}$,we can write $P = \frac{dRT}{M}$.
Given: $d = 8 \, kg \, m^{-3}$,$T = -40 + 273.15 = 233.15 \, K$,$R = 8.314 \, J \, K^{-1} \, mol^{-1}$,and $M = 0.0365 \, kg \, mol^{-1}$.
Substituting the values: $P = \frac{8 \times 8.314 \times 233.15}{0.0365} \, Pa$.
$P = \frac{15511.45}{0.0365} \, Pa \approx 4.25 \times 10^{5} \, Pa$.
364
MediumMCQ
If the density of dioxygen gas at $STP$ is $1.43 \, g \, L^{-1}$,calculate its density at $17 \, ^\circ C$ and $800 \, torr$ pressure.
A
$1.29 \, g \, L^{-1}$
B
$1.417 \, g \, L^{-1}$
C
$1.52 \, g \, L^{-1}$
D
$1.35 \, g \, L^{-1}$

Solution

(B) The density $d$ of an ideal gas is given by the formula $d = \frac{PM}{RT}$.
At $STP$,$P_1 = 1 \, atm = 760 \, torr$,$T_1 = 273.15 \, K$,and $d_1 = 1.43 \, g \, L^{-1}$.
At the new condition,$P_2 = 800 \, torr$,$T_2 = 17 + 273.15 = 290.15 \, K$.
Since $M$ and $R$ are constant,we have $\frac{d_1 T_1}{P_1} = \frac{d_2 T_2}{P_2}$.
Rearranging for $d_2$: $d_2 = d_1 \times \frac{P_2}{P_1} \times \frac{T_1}{T_2}$.
Substituting the values: $d_2 = 1.43 \times \frac{800}{760} \times \frac{273.15}{290.15}$.
$d_2 = 1.43 \times 1.0526 \times 0.9414 \approx 1.417 \, g \, L^{-1}$.
365
DifficultMCQ
Assuming the molar mass of air is $28.84 \, g \, mol^{-1}$,calculate the payload (lifting capacity) of a balloon of volume $10^6 \, L$ filled with $He$ at $27 \, ^\circ C$ and $1 \, atm$ pressure.
A
$1.01 \times 10^3 \, kg$
B
$1.10 \times 10^3 \, kg$
C
$1.01 \times 10^6 \, kg$
D
$1.10 \times 10^6 \, kg$

Solution

(A) The payload is the difference between the mass of air displaced by the balloon and the mass of $He$ gas inside the balloon.
Using the ideal gas equation $PV = nRT = (m/M)RT$,the mass $m = (PVM)/(RT)$.
Given: $P = 1 \, atm$,$V = 10^6 \, L$,$T = 27 + 273 = 300 \, K$,$R = 0.0821 \, L \, atm \, K^{-1} \, mol^{-1}$.
Mass of air displaced $(m_{air})$ = $(1 \times 10^6 \times 28.84) / (0.0821 \times 300) \approx 1170.36 \, kg$.
Mass of $He$ inside $(m_{He})$ = $(1 \times 10^6 \times 4) / (0.0821 \times 300) \approx 162.32 \, kg$.
Payload = $m_{air} - m_{He} = 1170.36 - 162.32 = 1008.04 \, kg \approx 1010 \, kg$.
366
MediumMCQ
$A$ gas at $5 \, bar$ pressure is heated from $0 \, ^\circ C$ to $546 \, ^\circ C$ and its volume is reduced to one-third of its initial volume. Calculate the final pressure. (in $, bar$)
A
$15$
B
$30$
C
$45$
D
$60$

Solution

(C) Using the combined gas law: $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$
Given: $P_1 = 5 \, bar$,$V_1 = V$,$T_1 = 0 + 273 = 273 \, K$
$T_2 = 546 + 273 = 819 \, K$,$V_2 = \frac{V}{3}$
Substituting the values: $\frac{5 \times V}{273} = \frac{P_2 \times (V/3)}{819}$
$P_2 = \frac{5 \times 819 \times 3}{273} = 5 \times 3 \times 3 = 45 \, bar$
367
MediumMCQ
What will be the molar volume of nitrogen $(N_2)$ and argon $(Ar)$ at $273.15 \ K$ and $1 \ atm$?
A
$22.4 \ L \ mol^{-1}$ for both
B
$22.4 \ L \ mol^{-1}$ for $N_2$ and $24.8 \ L \ mol^{-1}$ for $Ar$
C
$24.8 \ L \ mol^{-1}$ for both
D
$22.4 \ L \ mol^{-1}$ for $Ar$ and $24.8 \ L \ mol^{-1}$ for $N_2$

Solution

(A) According to the ideal gas law,$PV = nRT$. At standard temperature and pressure $(STP)$,defined as $273.15 \ K$ and $1 \ atm$,the molar volume of an ideal gas is approximately $22.4 \ L \ mol^{-1}$.
Since both nitrogen $(N_2)$ and argon $(Ar)$ behave nearly as ideal gases under these conditions,their molar volumes are approximately equal to $22.4 \ L \ mol^{-1}$ each.
368
Medium
The value of the universal gas constant $R$ is the same for all gases. What is its physical significance?

Solution

(N/A) The unit of $R$ depends upon the units in which $p$,$V$,and $T$ are measured,as $R = \frac{p \cdot V}{n \cdot T}$.
If pressure is measured in $Pa$ (Pascal),volume per mole is measured in $m^3 \cdot mol^{-1}$,and temperature is measured in $K$ (Kelvin),then the units of $R$ are $Pa \cdot m^3 \cdot K^{-1} \cdot mol^{-1}$,which is equivalent to $J \cdot mol^{-1} \cdot K^{-1}$.
Since $J$ (Joule) defines the unit of work done,$R$ represents the work done by the gas per mole per Kelvin.
369
MediumMCQ
According to Boyle's law,what are the two isothermal graphs and what is their nature?
A
Graph of $p$ vs $V$ is a straight line and $p$ vs $1/V$ is a curve.
B
Graph of $p$ vs $V$ is a curve and $p$ vs $1/V$ is a straight line passing through the origin.
C
Both graphs are straight lines.
D
Both graphs are curves.

Solution

(B) According to Boyle's law,$p \propto 1/V$ at constant temperature.
$(i)$ The graph of $p$ vs $V$ is a rectangular hyperbola,which is a curve.
$(ii)$ The graph of $p$ vs $1/V$ is a straight line passing through the origin because $p = k(1/V)$,where $k$ is a constant.
370
MediumMCQ
What is the effect of temperature change on the Boyle's law isotherm graph?
A
The slope remains constant.
B
The constant $K$ changes with temperature.
C
The graph shifts towards the origin.
D
The pressure becomes independent of temperature.

Solution

(B) According to Boyle's law,$PV = K$ (where $K$ is a constant).
The value of the constant $K$ depends on the temperature $T$.
As the temperature increases,the value of $K$ increases,causing the isotherm to shift away from the origin.
Therefore,for different temperatures $T_3 > T_2 > T_1$,the slopes of the isotherms increase in the same order.
371
EasyMCQ
At a temperature of $300 \ K$,if the pressure of $0.09 \ mol$ of a gas is halved,what will be its volume?
A
$V_2 = 2V_1$
B
$V_2 = V_1 / 2$
C
$V_2 = V_1$
D
$V_2 = 4V_1$

Solution

(A) According to Boyle's Law,at constant temperature and amount of gas,$P_1V_1 = P_2V_2$.
Given that the pressure is halved,$P_2 = P_1 / 2$.
Substituting this into the equation: $P_1V_1 = (P_1 / 2) \times V_2$.
Therefore,$V_2 = 2V_1$.
Thus,the volume becomes double the initial volume.
372
MediumMCQ
What does Boyle's Law prove quantitatively? Why?
A
It proves that gases are highly compressible.
B
It proves that gases are incompressible.
C
It proves that pressure is independent of volume.
D
It proves that temperature is constant.

Solution

(A) Boyle's Law quantitatively proves that,"Gases are highly compressible."
This is because when a given mass of gas is compressed,the same number of molecules occupies a smaller space,meaning that gases become denser at higher pressures.
373
EasyMCQ
What will be the effect on the density of $0.09 \ mol$ of a gas at $300 \ K$ if its pressure is increased?
A
Density increases
B
Density decreases
C
Density remains constant
D
Density becomes zero

Solution

(A) According to the ideal gas equation,$PV = nRT$ and $d = \frac{PM}{RT}$,where $d$ is density,$P$ is pressure,$M$ is molar mass,$R$ is the gas constant,and $T$ is temperature.
At constant temperature $(T)$ and constant molar mass $(M)$,the density $(d)$ is directly proportional to the pressure $(P)$: $d \propto P$.
Therefore,increasing the pressure of the gas will result in an increase in its density.
374
MediumMCQ
For $0.09 \, \text{mol}$ of $CO_2$ at $300 \, K$,the volume is $112.0 \times 10^{-3} \, m^3$ at a pressure of $2.0 \times 10^4 \, Pa$. What will be the volume at a pressure of $4.0 \times 10^4 \, Pa$?
A
$56.0 \times 10^{-3} \, m^3$
B
$112.0 \times 10^{-3} \, m^3$
C
$224.0 \times 10^{-3} \, m^3$
D
$28.0 \times 10^{-3} \, m^3$

Solution

(A) According to Boyle's Law,for a fixed amount of gas at a constant temperature,$P_1V_1 = P_2V_2$.
Given:
$P_1 = 2.0 \times 10^4 \, Pa$
$V_1 = 112.0 \times 10^{-3} \, m^3$
$P_2 = 4.0 \times 10^4 \, Pa$
Substituting the values:
$V_2 = \frac{P_1V_1}{P_2} = \frac{2.0 \times 10^4 \, Pa \times 112.0 \times 10^{-3} \, m^3}{4.0 \times 10^4 \, Pa}$
$V_2 = 0.5 \times 112.0 \times 10^{-3} \, m^3 = 56.0 \times 10^{-3} \, m^3$.
375
Medium
The following graphs are based on Boyle's Law at constant mass and temperature. Describe what each graph represents.
Question diagram

Solution

(N/A) Boyle's Law states that at constant temperature,the pressure of a fixed amount of gas is inversely proportional to its volume ($p \propto 1/V$ or $pV = k$).
$(i)$ Plot of $V$ vs $p$: Shows an isothermal curve (hyperbola) representing $V \propto 1/p$.
(ii) Plot of $V$ vs $1/p$: Shows a straight line passing through the origin,confirming $V = k(1/p)$.
(iii) Plot of $p$ vs $1/V$: Shows a straight line passing through the origin,confirming $p = k(1/V)$.
(iv) Plot of $\log_{10} p$ vs $\log_{10} V$: Since $pV = k$,taking log on both sides gives $\log p + \log V = \log k$,or $\log p = -\log V + \log k$. This is a straight line with a slope of $-1$.
$(v)$ Plot of $p$ vs $V$ at different temperatures: Shows isotherms where $p$ decreases as $V$ increases. Higher temperature curves are further from the origin $(T_3 > T_2 > T_1)$.
(vi) Plot of $p$ vs $1/V$ at different temperatures: Shows straight lines passing through the origin. The slope $(k = nRT/V)$ increases with temperature,so $T_3 > T_2 > T_1$ (Note: The image label $T_3 < T_2 < T_1$ in the provided diagram is physically incorrect for the slope of $p$ vs $1/V$ at constant $n$).
376
MediumMCQ
For a fixed amount of gas at constant pressure,provide the plot of volume $(V)$ versus temperature $(T)$ in Kelvin. What does it represent?
A
It represents Boyle's Law.
B
It represents Charles's Law.
C
It represents Avogadro's Law.
D
It represents Gay-Lussac's Law.

Solution

(B) The plot of volume $(V)$ versus temperature $(T)$ at constant pressure for a fixed amount of gas is a straight line passing through the origin.
$\therefore V \propto T$ (at constant $p$ and $n$)
This represents Charles's Law,which states that the volume of a fixed mass of gas is directly proportional to its absolute temperature at constant pressure.
377
Difficult
State the combined gas law and the ideal gas equation.

Solution

(N/A) The combined gas law is given by $\frac{p_{1}V_{1}}{T_{1}} = \frac{p_{2}V_{2}}{T_{2}}$.
The ideal gas equation is given by $pV = nRT$,where $p$ is pressure,$V$ is volume,$n$ is the number of moles,$R$ is the universal gas constant,and $T$ is the temperature.
378
DifficultMCQ
By what other name is the ideal gas equation known? Why?
A
Equation of state
B
Equation of motion
C
Equation of energy
D
Equation of change

Solution

(A) The ideal gas equation is also known as the $Equation \ of \ state$.
This is because the equation $pV = nRT$ describes the relationship between the four variables $p, V, n,$ and $T$ that define the state of a gas.
379
Medium
What is the value of $R$ in the ideal gas equation $pV = nRT$ in units of $bar \ L \ mol^{-1} \ K^{-1}$? Calculate it.

Solution

(N/A) The value of $R$ is $0.08314 \ bar \ L \ mol^{-1} \ K^{-1}$.
From the ideal gas equation,$pV = nRT$,we have $R = \frac{pV}{nT}$.
At standard temperature and pressure $(STP)$,$1 \ mol$ of an ideal gas occupies $22.71 \ L$ at $1 \ bar$ pressure and $273.15 \ K$.
Substituting these values: $R = \frac{(1 \ bar)(22.71 \ L)}{(1 \ mol)(273.15 \ K)}$.
$R = 0.083141 \ bar \ L \ mol^{-1} \ K^{-1}$.
Thus,$R \approx 8.314 \times 10^{-2} \ bar \ L \ mol^{-1} \ K^{-1}$.
380
Medium
What is the molar volume of a gas? What is its value taken as?

Solution

(N/A) The molar volume of a gas is defined as the volume occupied by $1 \, \text{mol}$ of an ideal gas at $STP$.
At $STP$ ($273.15 \, K$ temperature and $1 \, \text{bar}$ pressure),the volume of $1 \, \text{mol}$ of an ideal gas is $22.710981 \, L \, \text{mol}^{-1}$,which is its molar volume.
381
MediumMCQ
If $R = 8.314$,express it with its units.
A
$8.314 \ J \ K^{-1} \ mol^{-1}$
B
$8.314 \ L \ atm \ K^{-1} \ mol^{-1}$
C
$8.314 \ cal \ K^{-1} \ mol^{-1}$
D
$8.314 \ erg \ K^{-1} \ mol^{-1}$

Solution

(A) The universal gas constant $R$ has a value of $8.314 \ J \ K^{-1} \ mol^{-1}$ in $SI$ units.
It can also be expressed as $8.314 \ Pa \ m^3 \ K^{-1} \ mol^{-1}$ since $1 \ J = 1 \ Pa \ m^3$.
382
Easy
If $R = 0.082$,write it with its units and state the value with full precision.

Solution

(N/A) $(i)$ $R = 0.082 \, L \, atm \, K^{-1} \, mol^{-1}$
$(ii)$ $R = 8.20 \times 10^{-2} \, L \, atm \, K^{-1} \, mol^{-1}$
The value of $R$ with full precision is:
$(iii)$ $R = 8.20578 \times 10^{-2} \, L \, atm \, K^{-1} \, mol^{-1}$
383
Medium
What is the molar volume of an ideal gas at $STP$ (or $NTP$) and $SATP$?

Solution

(N/A) The molar volume of an ideal gas at $STP$ $(0 \, ^{\circ}C, 1 \, bar)$ is $22.71098 \, L \, mol^{-1}$.
Previously,at $STP$ $(0 \, ^{\circ}C, 1 \, atm)$,the molar volume was taken as $22.413996 \, L \, mol^{-1}$.
The molar volume of an ideal gas at $SATP$ $(25 \, ^{\circ}C, 1 \, bar)$ is $24.787 \, L \, mol^{-1}$.
384
MediumMCQ
At constant temperature and pressure,what is the volume of $n$ moles of different gases?
A
It depends on the nature of the gas
B
It is the same for all gases
C
It is different for all gases
D
It is zero

Solution

(B) According to the ideal gas equation,$pV = nRT$.
Rearranging for volume,we get $V = \frac{nRT}{p}$.
Since $n$,$R$,$T$,and $p$ are constant,the volume $V$ is the same for all gases regardless of their chemical nature.
385
Medium
What is the relationship between the molecular mass,density,and volume of a gas?

Solution

(N/A) For a gas,the relationship between its molecular mass $(M)$,volume $(V)$,and density $(d)$ is given by the ideal gas equation $PV = nRT$.
Since $n = \frac{m}{M}$,where $m$ is the mass of the gas,we have $PV = \frac{m}{M}RT$.
Rearranging for density $(d = \frac{m}{V})$,we get $d = \frac{PM}{RT}$.
Thus,at constant temperature and pressure,the density of a gas is directly proportional to its molecular mass $(d \propto M)$.
386
Medium
State Avogadro's Law and Gay-Lussac's Law.

Solution

(N/A) Avogadro's Law: Equal volumes of all gases at the same temperature and pressure contain an equal number of molecules. Mathematically,$V \propto n$ (at constant $T$ and $p$).
Gay-Lussac's Law: At a constant volume,the pressure of a fixed amount of a gas is directly proportional to its absolute temperature. Mathematically,$p \propto T$ (at constant $n$ and $V$).
387
MediumMCQ
State Charles's Law.
A
Pressure is inversely proportional to volume at constant temperature.
B
Volume is directly proportional to absolute temperature at constant pressure.
C
Volume is inversely proportional to absolute temperature at constant pressure.
D
Pressure is directly proportional to absolute temperature at constant volume.

Solution

(B) Charles's Law states that for a fixed mass of an ideal gas,the volume is directly proportional to its absolute temperature at constant pressure.
Mathematically,$V \propto T$ (at constant $P$ and $n$).
This can be expressed as $\frac{V}{T} = k$,where $k$ is a constant.
388
MediumMCQ
If the temperature of a fixed mass of gas is increased by $1\,^{\circ}C$ at constant pressure,what will be the new volume of the gas?
A
$V_{0} + \frac{1}{273.15} V_{0}$
B
$V_{0} + \frac{1}{273.15}$
C
$V_{0} \times \frac{1}{273.15}$
D
$V_{0} - \frac{1}{273.15} V_{0}$

Solution

(A) According to Charles's Law,for a fixed mass of gas at constant pressure,the volume $V_t$ at temperature $t\,^{\circ}C$ is given by $V_t = V_0 \left(1 + \frac{t}{273.15}\right)$.
Given that the temperature is increased by $1\,^{\circ}C$,we substitute $t = 1$ into the equation.
Therefore,the new volume $V_t = V_0 \left(1 + \frac{1}{273.15}\right) = V_0 + \frac{1}{273.15} V_0$.
389
EasyMCQ
If the temperature of a gas is increased by $1\,^oC$ while keeping the pressure and the amount of gas constant,what is the change in the original volume of the gas?
A
It increases by $\frac{1}{273.15}$ of its original volume.
B
It decreases by $\frac{1}{273.15}$ of its original volume.
C
It increases by $273.15$ times its original volume.
D
It remains constant.

Solution

(A) According to Charles's Law,$V \propto T$ at constant pressure and amount of gas.
For a temperature change of $1\,^oC$,the volume changes by a factor of $\frac{1}{273.15}$ of the volume at $0\,^oC$.
Therefore,the volume increases by $\frac{1}{273.15}$ of its original volume.
390
Easy
On what factors do the values of the gas constant $R$ depend? What is its unit?

Solution

(N/A) The value of the gas constant $R$ depends on the units of the variables $p$,$V$,$n$,and $T$ used in the ideal gas equation $pV = nRT$.
The unit of $R$ is derived based on the units of $p$,$V$,$n$,and $T$ in the equation $pV = nRT$.
391
MediumMCQ
If the density of neon gas at $350 \ K$ is $0.9 \ g \ L^{-1}$,calculate the pressure of the gas. (in $bar$)
A
$1.303$
B
$0.900$
C
$2.500$
D
$0.500$

Solution

(A) The ideal gas equation is given by $PV = nRT$. Since $n = \frac{m}{M}$,we have $PV = \frac{m}{M}RT$. Rearranging for pressure $P$,we get $P = \frac{m}{V} \times \frac{RT}{M} = \frac{dRT}{M}$.
Given: Density $d = 0.9 \ g \ L^{-1}$,Temperature $T = 350 \ K$,Molar mass of Neon $M = 20.18 \ g \ mol^{-1}$,Gas constant $R = 0.08314 \ L \ bar \ K^{-1} \ mol^{-1}$.
Substituting the values: $P = \frac{0.9 \times 0.08314 \times 350}{20.18} \approx 1.297 \ bar \approx 1.303 \ bar$ (using standard approximations).
392
MediumMCQ
What is the value of the ratio of density $(d)$ to molar mass $(M)$ for an ideal gas?
A
$P/RT$
B
$RT/P$
C
$PM/RT$
D
$RT/PM$

Solution

(A) From the ideal gas equation,$PV = nRT$.
Since $n = \frac{m}{M}$,we have $PV = \frac{m}{M} RT$.
Rearranging the terms,$\frac{m}{V} = \frac{PM}{RT}$.
Since density $d = \frac{m}{V}$,we get $d = \frac{PM}{RT}$.
Therefore,the ratio $\frac{d}{M} = \frac{P}{RT}$.
393
EasyMCQ
Under what conditions does an ideal gas have maximum density?
A
High pressure and high temperature
B
Low pressure and low temperature
C
High pressure and low temperature
D
Low pressure and high temperature

Solution

(C) The density $(d)$ of an ideal gas is given by the formula $d = \frac{MP}{RT}$.
From this relation,it is clear that density is directly proportional to pressure $(P)$ and inversely proportional to temperature $(T)$.
Therefore,to achieve maximum density,the gas must be at high pressure and low temperature.
394
MediumMCQ
If the density ratio of a gas is $1:2$ and the temperature ratio is $2:1$,what will be the ratio of their pressures?
A
$1:1$
B
$1:2$
C
$2:1$
D
$4:1$

Solution

(A) From the ideal gas equation,$PV = nRT$,we know $PV = (\frac{m}{M})RT$,which gives $P = (\frac{d}{M})RT$,where $d$ is the density.
Therefore,$P = \frac{dRT}{M}$.
Given $\frac{d_1}{d_2} = \frac{1}{2}$ and $\frac{T_1}{T_2} = \frac{2}{1}$.
Taking the ratio of pressures: $\frac{P_1}{P_2} = (\frac{d_1}{d_2}) \times (\frac{T_1}{T_2}) = \frac{1}{2} \times \frac{2}{1} = \frac{1}{1}$.
Thus,the ratio of their pressures is $1:1$.
395
EasyMCQ
Define the gas constant $R$ in terms of work.
A
$R = \frac{PV}{nT}$
B
$R = \frac{W}{nT}$
C
$R = \frac{n}{WT}$
D
$R = \frac{T}{nW}$

Solution

(B) The ideal gas equation is given by $PV = nRT$.
From the first law of thermodynamics,work done $W$ by an ideal gas during expansion is related to the pressure-volume product.
Since $PV$ has the dimensions of energy or work,we can express the gas constant $R$ as $R = \frac{PV}{nT}$.
Substituting work $W$ for $PV$,we get $R = \frac{W}{nT}$.
Thus,$R$ represents the work done per mole per unit temperature change.
396
Difficult
Provide the different values and units of the universal gas constant $R$.

Solution

(N/A) The universal gas constant $R$ is defined by the ideal gas equation $PV = nRT$,which implies $R = \frac{PV}{nT}$. Its value depends on the units used for pressure,volume,and temperature. The following table summarizes the common values of $R$:
Condition Value and Unit of $R$
$(i)$ Pressure in $atm$,Volume in $L$ $0.0821 \ L \ atm \ K^{-1} \ mol^{-1}$
$(ii)$ Pressure in $bar$,Volume in $L$ $0.08314 \ L \ bar \ K^{-1} \ mol^{-1}$
$(iii)$ $SI$ Units (Pressure in $Pa$,Volume in $m^3$) $8.314 \ J \ K^{-1} \ mol^{-1}$
$(iv)$ Energy in $calories$ $1.987 \ cal \ K^{-1} \ mol^{-1}$
397
Medium
What do the gas laws,such as Boyle's law,Charles's law,etc.,state?

Solution

(N/A) These laws provide precise statements about experimental facts and tell us how a particular system behaves under different conditions.
Gas laws are useful for making predictions,such as how the pressure of a gas increases when it is compressed.
398
EasyMCQ
For an ideal gas,what is the nature of the $pV$ versus $p$ graph at a constant temperature?
A
$A$ straight line passing through the origin
B
$A$ straight line parallel to the $p$-axis
C
$A$ parabolic curve
D
$A$ hyperbolic curve

Solution

(B) According to Boyle's Law,for an ideal gas at constant temperature,$pV = \text{constant}$.
Therefore,the product $pV$ remains independent of the pressure $p$.
As a result,the graph of $pV$ versus $p$ is a straight line parallel to the $p$-axis.
399
EasyMCQ
When does $Z = 1$ occur?
A
For real gases at high pressure
B
For ideal gases
C
For real gases at low temperature
D
For all gases at all conditions

Solution

(B) The compressibility factor $Z$ is defined as $Z = \frac{pV}{nRT}$.
If $pV = nRT$,then $Z = 1$.
This condition is satisfied by ideal gases under all conditions of temperature and pressure.
400
EasyMCQ
Under what conditions does a gas behave ideally? Why?
A
High pressure and low temperature
B
Low pressure and high temperature
C
High pressure and high temperature
D
Low pressure and low temperature

Solution

(B) gas behaves ideally at low pressure and high temperature.
Under these conditions,the intermolecular forces of attraction become negligible,and the volume occupied by the gas molecules becomes negligible compared to the total volume of the gas.
Consequently,the van der Waals equation $(p + \frac{an^2}{V^2})(V - nb) = nRT$ reduces to the ideal gas equation $pV = nRT$ because the pressure correction term $\frac{an^2}{V^2} \approx 0$ and the volume correction term $nb \approx 0$.

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