GENERAL GAS EQUATION at a glance

 GENERAL GAS EQUATION

The General Gas Equation is a formula that shows the relationship between the pressure, volume, and temperature of a gas.

It is a combination of both Boyle’s and Charles law.

It is written as:

PV = K

T

P1V1  = P2V2 

   T             T

Explanation

The general gas equation combines the three gas laws:

• Boyle’s Law (pressure and volume)

• Charles’ Law (volume and temperature)

• Pressure Law (pressure and temperature)

It helps us calculate any one of the gas properties if the others are known.

Example

If the pressure, volume, and temperature of a gas are known, the number of moles can be calculated using:

n = PV
      RT

THEORY QUESTIONS 

1. What is the volume at s.t.p of a fixed mass of a gas that occupies 700cm³ at 25^oC and 0.84 x 10⁵ Nm^-2pressure?

    Solution:

   T₁ = 273K, P₁ = 1.01 x 10⁵Nm^-2, T₂ = 25^oC = (25 + 273) = 298K, P₂ = 0.84 x 10⁵Nm^-2,

    V₂ = 700cm³, V₁ =?

   Using the general gas equation

P₁V₁ = P₂V₂
   T₁        T₂

     V₁ = P₂V₂T₁ = 0.84 x 10⁵Nm^-2 x 700cm³ x 273K = 533.337 =533cm³
              P₁T₂          1.01 x 10⁵Nm^-2 x 298K

     = 0.84 x 10⁵Nm^-2 x 700cm³ x 273K = 533.337 
                       1.01 x 10⁵Nm^-2 x 298K

                                           =533cm³
              

Conclusion

The general gas equation is very useful in solving problems involving gases in chemistry.

OBJECTIVE QUESTIONS 

1. The general gas equation is expressed as
   A. ( PV = RT )
   B. ( PV = nRT )
   C. ( V = nRT )
   D. ( P = nRT )

2. In the general gas equation ( PV = nRT ), the symbol R represents
   A. rate constant
   B. gas density
   C. universal gas constant
   D. pressure constant

3. Which of the following quantities must be in Kelvin when using the gas equation?
   A. Pressure
   B. Volume
   C. Temperature
   D. Amount of gas

4. The SI unit of pressure used in the general gas equation is
   A. atmosphere
   B. mmHg
   C. pascal
   D. bar

5. The general gas equation combines which gas laws?
   A. Boyle’s and Charles’ laws only
   B. Boyle’s, Charles’ and Graham’s laws
   C. Boyle’s, Charles’ and Avogadro’s laws
   D. Dalton’s and Avogadro’s laws

6. The value of the universal gas constant R is approximately
   A. 0.082 J mol⁻¹ K⁻¹
   B. 8.31 J mol⁻¹ K⁻¹
   C. 82.06 J mol⁻¹ K⁻¹
   D. 1.00 J mol⁻¹ K⁻¹

7. Which of the following is the unit of R when pressure is in pascals?
   A. L atm mol⁻¹ K⁻¹
   B. J mol⁻¹ K⁻¹
   C. cm³ atm mol⁻¹ K⁻¹
   D. Nm⁻² mol⁻¹

8. If the temperature of a gas increases while pressure is constant, the volume will
   A. decrease
   B. remain constant
   C. increase
   D. become zero

9. One mole of an ideal gas occupies 22.4 dm³ at
   A. 0°C and 1 atm
   B. 25°C and 1 atm
   C. 0°C and 760 Pa
   D. 273°C and 1 atm

10. The general gas equation is most accurate when gases
    A. are at very high pressure
    B. are at very low temperature
    C. behave ideally
    D. are strongly interacting

11. In the equation ( PV = nRT ), the symbol n represents
    A. number of molecules
    B. number of atoms
    C. amount of gas in moles
    D. mass of gas

12. Which condition is necessary for gases to obey the general gas equation?
    A. High pressure and low temperature
    B. Low pressure and high temperature
    C. Presence of strong intermolecular forces
    D. Gas must be liquid

13. If pressure is doubled and temperature remains constant, the volume will
    A. double
    B. halve
    C. remain the same
    D. become zero

14. The general gas equation is also known as the
    A. combined gas law
    B. Dalton’s law
    C. ideal gas equation
    D. Graham’s law

15. Which of the following is NOT an assumption of the kinetic theory of gases?
    A. Gas particles are in constant motion
    B. Gas molecules occupy negligible volume
    C. There are strong forces between molecules
    D. Collisions are elastic

16. A gas has a volume of 2 dm³ at 300 K. What will be its volume at 600 K if pressure is constant?
    A. 1 dm³
    B. 2 dm³
    C. 3 dm³
    D. 4 dm³

17. Increasing the number of moles of a gas at constant temperature and pressure will
    A. decrease volume
    B. not affect volume
    C. increase volume
    D. decrease pressure

18. Which of the following quantities is directly proportional to pressure according to the gas equation?
    A. Volume
    B. Temperature
    C. Amount of gas
    D. Both B and C

19. The equation ( \frac{PV}{T} = \text{constant} ) is derived from
    A. Boyle’s law
    B. Charles’ law
    C. Combined gas law
    D. Graham’s law

20. The general gas equation is mainly used to
    A. calculate molecular mass only
    B. explain diffusion
    C. relate pressure, volume, temperature and amount of gas
    D. describe electrolysis

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