Charles' Law
Charles' law states that, at a constant pressure, the volumeof a mixed amount of gas is directly proportional to its absolute temperature:
Avogadro law is sometime also called as Avogadro hypothesis or Avogadro’s principle. It is an experimental law which was given in 1811 by Amedeo Avogadro. Statement: Under constant temperature and pressure, equal volumes of all the gases contains equal no of molecules. Boyle's law, Charles's law, and Gay-Lussac's law form the combined gas law. The three gas laws in combination with Avogadro's law can be generalized by the ideal gas law.
Where k is a constant unique to the amount of gas and pressure. Just as with Boyle's law, Charles' law can be expressed in its more useful form:
| = |
The subscripts 1 and 2 refer to two different sets of conditions, just as with Boyle's law.
Why must the temperature be absolute? If temperature is measured on a Celsius (non absolute) scale, T can be negative. If we plug negative values of T into the equation, we get back negative volumes, which cannot exist. In order to ensure that only values of V≥ 0 occur, we have to use an absolute temperature scale where T≥ 0. The standard absolute scale is the Kelvin(K) scale. The temperature in Kelvin can be calculated via Tk = TC + 273.15. A plot of the temperature in Kelvin vs. volume gives :As you can see from , Charles' law predicts that volume will be zero at 0 K. 0 K is the absolutely lowest temperature possible, and is called absolute zero.
Avogadro's Law
Avogadro's law states that the volume of a gas at constant temperature and pressure is directly proportional to the number of moles of gas present. It's mathematical representation follows:
k is a constant unique to the conditions of P and T. n is the number of moles of gas present.
1 mole (mol) of gas is defined as the amount of gas containing Avogadro's number of molecules. Avogadro's number (NA) is
| NA = 6.022×1023 |
1 mol of any gas at 273 K (0_C) and 1 atm has a volume of 22.4 L. The conditions 273 K and 1 atm are the standard temperature and pressure (STP). STP should not be confused with the less common standard atmospheric temperature and pressure (SATP), whichcorresponds to a temperature of 298 K and a pressure of 1 bar.
The numbers 22.4 L, 6.022×1023, and the conditions of STP should be near and dear to your heart. Memorize them if you haven't already.
The Ideal Gas Law
Charles', Avogadro's, and Boyle's laws are all special cases of the ideal gas law:
T must always be in Kelvin. n is almost always in moles.R is the gas constant. The value of R depends on the units of P, V and n. Be sure to ask your instructor which values you should memorize.
| Units | Value of R |
| 0.08206 | |
| 8.314 | |
| 8.314 | |
| 1.987 | |
| 62.36 |
The ideal gas law is the equation you must memorize for gases. It not only allows you to relate P, V, n and T, but can replace any of the three classical gas laws in a pinch. For example, let's say you're given constant values of P and n, but forget how Charles' law relates V and T. Rearrange the ideal gas law to separate the constants and unknowns:
Voila! We have derived Charles' law from the ideal gas law. n,
R, and T are constants, so is just the constant k from Charles' law.The ideal gas law is also useful for those rare occasion when you forget the value of a constant. Let's say I forgot the value of R in . If I remember that a mole of gas has a volume of 22.4 L at STP (760 torr, 273 K), I can rearrange PV = nRT to solve for R in the desired units. It is much more efficient to memorize the values, but it is comforting to know that you can always fall back on good old PV = nRT.
Applying the Ideal Gas Law
Ideal gas law problems tend to introduce a lot of different variables and numbers. The sheer amount of information can be confusing, and it is wise to develop a systematic method to solve them:
1) Jot down the values of P, V, n, and T. If the question says that one of these variables is constant or asks you to find the value of one or the other, make a note of it. Every time you encounter a numerical value or variable, try to fit it into your PV = nRT scheme.
2) Rearrange PV = nRT such that the unknowns and knowns are on opposite sides of the '=' sign. Make sure that you are comfortable with the algebra involved.
3) Convert to the appropriate units. Generally you'll want to deal with SI units (m3, Pa, K, mol). There will be times that non-SI units will be more convenient. In these cases, remember that T must always be in Kelvin. Make sure to select the correct value and units of R.
4) Plug in values and solve for the unknown(s). Ideal gas problems involve a great deal of algebra. The only way to master this type of problem is to practice. Use the problems provided at the end of this section and your textbook until the manipulations of PV = nRT become familiar.
5) Take a step back and check your work. The easiest way to do this is to carry all of the units through your ideal gas calculations. When you're about to solve the equation, make sure that the units on both sides of the '=' sign are equivalent. For simpler problems, it is also worthwhile to make sure that your answer makes sense. For example, if n, R, and T are constant and Prises, make sure that V decreases. It only takes a few seconds, and can save you from some embarrassing mistakes. The usefulness of such commonsense checks decreases as the questions get more complex. For any problem where more than two variables change, you're better off trusting the ideal gas law and your own algebra.
The best advice I can give you is to practice. The more problems you do, the more comfortable you will be with the ideal gas law.
MCQ on gas laws
MCQ General Knowledge on Behavior of Gas Boyle’s Law, Charles’s Law Avogadro’s Law Objective short Questions and Answers for class 9 10 and aspirants who are preparing for competitive govt job examinations like SSC, CGL, MTS, IAS, UPSC, Railway, Banking, Defence, Police CDS, etc..
[MCQ.1] The constant quantity of Boyle’s Law is
A: Only mass of the gas
B: Only temperature of a gas
C: Mass and Pressure of a gas
D: Mass and temperature of a gas
Answer
D: Mass and temperature of a gas.
[MCQ.2] Let the pressure P and volume V for a certain gas. If the pressure is increased by 25% at a constant temperature, then what would be the volume of the gas?
A: 0.6V
B: 0.75V
C: 0.8V
D: 0.85V
Answer
0.8V
[MCQ.3] What is the nature of the pressure-volume (P-V) graph in Boyle’s Law?
A: Straight Line;
B: Circle:
C: Elliptical;
D: Rectangular Hyperbola:
Answer
Rectangular Hyperbola.
[MCQ.4] What is the nature of the pressure-volume vs Pressure (PV vs P) graph in Boyle’s Law?
A: Straight Line parallel to P axis;
B: Straight line parallel to PV axis:
C: Elliptical;
D: Hyperbola:
Answer:
Straight-line parallel to the P axis.
[MCQ.5] The unit of pressure in the SI system is-
A: N
B: N-m
C: N-m2
D: N/m2
Answer:
N/m2
[MCQ.6] 1 m3 = ______ cm3
A: 100
B: 103
C:105
D: 106
Answer
D: 106
[MCQ.7] If the pressure of a certain amount of gas is reduced to 1/4th of its initial pressure at a fixed temperature, then what would be its final volume?
A: 2 times
B: 3 times
C: 4 times
D: 6 times
Answer
C: 4 times
[MCQ.8] If the pressure is increased by 2 times of a certain amount of gas at a fixed temperature, then what would be its final volume?
A: Double
B: One half
C: Tripple
D: One fourth
Answer
B: One half
[MCQ.9] Suppose, at for a gas having constant mass the volume is V0 at temperature 0 oC. What would be its final volume at 100 oC if the pressure remains constant?
A: (293/273)V0
B:(283/273)V0
C: (303/273)V0
D: (373/273)V0
Answer
(303/273)V0
[MCQ.10] For a given mass of an ideal gas at constant pressure, the graph V – t (t in Celcius scale), intersect the temperature axis at –
A: – 273 oC
B: 0 oC
C: 273 oC
D: Do not intersect.
Answer
A: – 273 oC
[MCQ.11] In which scale of temperature, the temperature can not be negative?
A: Celcius Scale
B: Fernheight Scale
C: Absolute Scale
D: All of the above
Answer
C: Absolute Scale
[MCQ.12] The Freezing point of water in absolute scale is-
A: 0 K
B: 273 K
C: 212 K
D: None of the above;
Answer
B: 273 K
[MCQ.13] If the temperature is increased from 0 oC to 30 oC at a constant pressure of gas having fixed mass, then the ratio of initial and final volume will be –
A: 91 : 101
B: 91 : 100
C: 91 : 111
D: 91 : 121
Answer
A: 91 : 101
[MCQ.14] The constant quantity(s) in Charle’s Law is (are)-
A: Temperature
B: Volume
C: Pressure and Mass of gas
D: Temperature and Mass of gas
Answer
Pressure and Mass of a gas.
[MCQ.15] The nature of the V-t (t in Celsius scale) graph in Charle’s law is-
A: Straight line
B: Circle
C: Parabola
D: Hyperbola
Answer
Straight line
[MCQ.16] At which temperature the volume of gas reduces to Zero?
A: 0 K
B: 0 oC
C: 273 oC
D: 273 K
Answer
A: 0 K
[MCQ.17] Which Scientist discovered the absolute scale of temperature?
A: Charles
B: Boyle
C: Kelvin
D: Gay-Lussac.
Answer
Kelvin
[MCQ.18] At which temperature the real gas behaves as an ideal gas?
A: At high pressure and low temperature;
B: At low-pressure and high temperature;
C: At low pressure and low temperature;
D: AT high pressure and high temperature;
Answer
B: At high temperature and low pressure;
[MCQ.19] The molar mass of water is –
A: 16 g
B: 20 g
C: 18 g
D: 44 g
Answer
C: 18 g
[MCQ.20] The mass of 5 mol of Hydrogen gas is-
A: 5 g
B: 10 g
C: 18 g
D: 27 g
Answer
B: 10 g
[MCQ.21] In the case of collision of two gas molecule of an ideal gas –
A: The linear momentum is conserved only;
B: The kinetic energy is conserved only;
C: Linear momentum and kinetic energy both conserve;
D: Linear momentum and kinetic energy both are not conserved;
Answer
C: Linear momentum and kinetic energy both are conserved.
[MCQ.22] The energy of the molecules of an ideal gas is –
A: Only potential energy;
B: Only kinetic energy;
C: Kinetic energy + potential energy;
D: Kinetic energy – potential energy;
Answer
B: Only kinetic energy;
[MCQ.23] Which is the Ideal Gas Equation from the following?
A: PV = mc2;
B: PV = mgh;
C: PV = nRT;
D: PV = mSt;
Answer
C: PV = nRT;
[MCQ.24] Which is the constant quantity in Ideal Gas Equation?
A: Pressure P
B: Volume V
C: R
D: Temperature
Answer
C: R
Boyle's Law Avogadro's Law And Charles Law
[MCQ.25] The value of Universal Gas Constant in CGS unit is –
A: 8.31 * 106
B: 8.31 * 107
C: 8.31 * 108
D: 8.31 * 109
Answer
B: B: 8.31 * 107
[MCQ.26] The dimension of the universal gas constant is –
A: M L2 T-1 N-1
B: M L-1 T-1 N-2K-1
C: M L2 T-1 N-2 K
D: M L-1 T-2 N-1 K-1
Answer
D: M L-1 T-2 N-1 K-1
[MCQ.27] According to the kinetic theory of gas, at which temperature the kinetic energy of a molecule of an ideal gas becomes zero?
A: — 273 oC
B: 0 oC
C: – 100 oC
D: 273 K
Answer
A: — 273 oC
[MCQ.28] 84 g of N2 = ______ g N2.
A: 1 g
B: 2 g
C: 3 g
D: 4 g
Answer
C: 3 g
[MCQ.29] Which of the following has the largest volume?
2 g of Hydrogen Gas, 28 g of Nitrogen Gas, 44 g of CO2 gas.
A: 2 g of Hydrogen Gas
B: 28 g of Nitrogen Gas
C: 44 g of CO2 gas
D: All gasses have the same volume.
Answer
D: All the gas has the same volume.
[MCQ.30] How many atoms are there in 1 mol of CO2 gas if the Avogadro number in N?
A: N
B: 2N
C: 3N
D: 4N
Answer
Boyle's Law Example
C: 3N
[MCQ.31] If the mass of 11.2 L of CO2 is 22g, then what is its atomic mass?
A: 22
B: 44:
C: 88
D: 11
Answer
B: 44
[MCQ.32] The mass of an O2 molecule is –
A: 5.31 * 10-23g
B: 10.62 * 10-23
C: 15.93 * 10-23
D: 2.65 * 10-23
Answer
5.31 * 10-23g
[MCQ.33] The number of molecules of 7g of N2 gas is-
A: 22.044 * 1023
B: 1.506 * 1023
C: 3.011 * 1023
D: 6.022 * 1023
Answer
1.506 * 1023
[MCQ.34] The volume of 2.2 g CO2 at 27 oC and 570 mm pressure is –
A: 4.83 L
B: 0.82 L
C: 3.82 L
D: 1.64 L
Answer
D: 1.64 L
[MCQ.35] At which condition the real gas deviated from the ideal gas?
A: At low temperature and low pressure
B: At Low pressure and high temperature;
C: At high pressure and low temperature;
D: At high pressure and high temperature;
Answer
At low temperature and high pressure.
[MCQ.36] The state of the equation for 7g of Oxygen gas is _
A: PV = 7RT
B: PV = (32/7)RT
C: PV = (7/32)RT
D: PV = 32RT
Answer
C: PV = (7/32)RT
[MCQ.37]If the pressure of a certain amount of gas is increased at a constant temperature, the density of the gas is –
A: Remain Constant;
B: Decreased;
C: Increased;
D: Can not be determined;
Answer
Increased
[MCQ.38] What would be the volume of 22g of Carbon dioxide at STP?
A: 11.2 L
B: 1.12 L
C: 22.4 L
D: 2.24 L
Answer
11.2 L
Boyle And Charles Law
[MCQ.39] The molar volume of any gas at STP is –
A: 22.4 L
B: 2.24 L
C: 44 L
D: 24.2 L
Answer
22.4 L
Download MCQ of Gas Laws – Boyle’s Law, Charles’s Law Avogadro’s Law