20 Physics -- Ideal Gas

In equations for ideal gas and thermodynamics , what is the difference between 'R' and 'r' .

1 Answers

Value of R is a constant for all gases while value of r is a variable for all gases but a constant for a specific gas.

Explanation:

Starting with the Ideal gas equation, PV = nRT.

R in the above equation stands for Universal Gas Constant whose value is a constant 8.314 J/mol-K for all gases.

However, when we put n = M/m where M represents total mass of gas present and m the molar mass of the gas.

The value of R/m = r or r = R/m is defined as the specific gas constant for a gas. Clearly, r is a constant for a particular gas only because value of m is different for different gases.

The fall in temperature of helium gas initially at 15oC when suddenly expanded to 8 times the original volume isa. 162oCb. 216oCc. 72oCd. 324oC

What is the differences between real gases and ideal gases? Explain in basis with kinetic theory of gases.

Following are the differences betweenr real gases and ideal gases:

Real Gases	Ideal Gases
Real gases follow gas laws under conditions of low pressure and high temperature.	Ideal gases follow gas laws under all conditions of temperature and pressure.
They have intermolecular forces of attraction.	They have negligible intermolecular force of attraction.
Collision of molecules of real gases are not perfectly elastic.	Collisions of molecules of real gases are perfectly elastic.

What mass of air exists in a 5 x 6 x 8 m³ room at 20°C? Take the average molecular mass of air to be 28 kg K-1 mol-1.

Mention the postulates of Kinetic theory of a gas and also explain the condition of a gas to behave as an ideal gas.

The postulates of kinetic theory of gas can be found here State the main postulates for Kinetic theory (askmattrab.com).

The condition for a gas to behave as an ideal gas can be found hereA student needed to use the ideal gas for a (askmattrab.com)

Helium gas occupies a volume of 0.04m^3 at a pressure of 2 x 10^5 Nm^-2 and temperature 300K. Calculate the mass of the helium and root mean square speed of its molecules. [ Relative molecular mass...

Although the r.m.s speed of a gas molecules is of the order of the speed of sound in that gas, yet on opening a bottle of ammonia in one corner of a room, its smell takes time in reaching the other...

The speed of molecules follows directly from measuring the pressure and density-you don’t need to know the size of molecules. In standard kinetic theory collisions with other molecules have always been ignored because the molecules were tiny. Though theyaren't. So the molecules are not going in straight line. Thus it takes time for the smell to spread in the room.

The pressure of a gas at -173C temperature is 1 atmosphere, keeping the volume constant, to what temperature should the gas be heated so that its pressure becomes 2 atm?

At Initial state

p_i= 1atm

T₀=-173^oc =100k

v_i=v

Finally

P_f= 2 atm

T_f= ?

V_f= v(constant)

By ideal gas law

PV = nRT

V = T/P = constant

T_i/p_i= T_f/p_f

T_f= T_i*P_f/p_i

=100*2/1

= 200k = -73^oc

Which has more molecules: a kilogram of hydrogen or a kilogram of oxygen?

A kilogram of hydrogen is having more molecules.

Explanation:
For hydrogen that value is 1.008. For oxygen it’s 16.00. That means however many times you can divide the mass by its molar mass, So for example 1000g (1kg) / 1.008 is approximately992 moles of hydrogen. And 1000g/16.00 is 62.5 moles of Oxygen. Now to put it all together, one mole is equal to 6.02x10^23 molecules so obviously since there are more moles of hydrogen, you would have a significantly larger amount of hydrogen.

What is the difference between a real and an ideal gas? Explain on the basis of the hypothesis of the kinetic theory.

Calculate the pressure in mm of mercury exerted by hydrogen gas if the number if moles per cm^3 is 6.8x10^15 and the root mean square speed of the molecules is 1.9x10^3m/s. [Avogadros constant = 6....

Give the formula that explains at 0K, all molecular motion ceases

At absolute zero the molecular motion of gases ceases to zero because, at this point volume of gases is said to zero.

Now at T = 0 K, kinetic energy=0

Therefore, the molecular motion is also zero.

Why are gas laws not obeyed at low temperature and high pressure?

The ideal gas law fails at low temperature and high-pressure becausethe volume occupied by the gas is quite small, so the inter-molecular distance between the molecules decreases.

Write the unit of Universal Gas Constant and give it's physical meaning.

The unit of the Universal Gas Constant, also known as the ideal gas constant, is joules per mole per kelvin (J/mol·K). Its physical meaning is that it relates the physical properties of gases, such as pressure, volume, and temperature, through the ideal gas law equation: PV = nRT.

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