The ideal gas law relates pressure P, volume V and temperature T of an ideal gas are by equation PV = nkBT, where n is the number of molecules of the gas, and kB is Bolztmann's constant. We can also write this as PV = NRT, where N denotes the number of moles of gas, and R is the gas constant. The ideal gas law is obeyed fairly well provided the density of the gas is not too high and these gases that obey it are called ideal gas. If the density is too high, the gas may condense to form a liquid, and the law fails in this case.
Ideal Gas Law
The constant volume gas thermometer is made of a bulb that is filled with a known fixed amount of a dilute gas attached to a mercury manometer. Now the bulb is brought in close contact with the source. The manometer attached to the bulb allows it to measure the exact pressure. The manometer contains a halfway filled mercury column and it is connected with a flexible tube to another partially filled column of mercury which is called the reservoir. Now the height of the mercury column is measured at the known temperature. Throughout this temperature measurement this height is fixed while the mercury in the reservoir is moved up or down.
This explains the gas thermometer. Now let us see how it works? This is where the ideal gas law comes in existence. The fundamental measurements of gas are done with pressure, P, volume, V and temperature, T. Also the SI Units of temperature is Kelvin; and T = t + 273.15 where t is in oC. The term pressure, volume and temperature of a gas are all interrelated and this interrelation was first explored by Robert Boyle. Boyle’s law states that when the temperature of a gas is kept constant, PV = Constant.
This explains the gas thermometer. Now let us see how it works? This is where the ideal gas law comes in existence. The fundamental measurements of gas are done with pressure, P, volume, V and temperature, T. Also the SI Units of temperature is Kelvin; and T = t + 273.15 where t is in oC. The term pressure, volume and temperature of a gas are all interrelated and this interrelation was first explored by Robert Boyle. Boyle’s law states that when the sample gas temperature held constant, PV = Constant.
French scientist Jacques Charles now came up with his law later named as Charles law. He discovered when the pressure of a gas is kept constant, the volume is related to the temperature by following equations
V/T = Constant.
These laws were later combined to yield one universal gas law known as the ideal gas law.
And the constant proportionality factor in this equation is the Universal Gas Constant, R ie, constant = nR.
where, n gives the number of moles of the gas in the sample
Absolute Zero Temperature
Absolute zero is the defined temperature at which a thermodynamics system has the lowest energy. It corresponds to −273.15°C on Celsius scale and to −459.67°F on the Fahrenheit scale. The notion that there is an ultimately lowest temperature was suggested by the behaviour of gases at a very low pressure. It was observed that gases seem to contract indefinitely as the temperature decreases. Also an ideal gas at constant pressure would reach zero volume at what is now called the absolute zero of temperature. Real gas in actual condenses to liquid or solid at some temperature higher than absolute zero that is why the ideal gas is only an assumption to real gas behavior.
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Significance of Absolute Zero
On extrapolating this graph, what we see is that between Pressure and temperature is shown below for different gases.
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Now irrespective of the nature of gas we see that, the graphs always intercept the x axis at a point we call the absolute zero. This point represents the beginning of the Kelvin scale i.e Zero K. In the Celsius scale, it corresponds to -273.5 oC. This is possibly the coldest temperature. As a molecule gets colder, it’s energy, movements and vibrations decrease in amplitude. As we keep cooling it, at a point the atom will reach a state of minimum internal energy where the atom has lost all its energy.Thus we cay that absolute zero is a state at which the enthalpy and entropy reach their minimum value and it the lowest limit on temperature scale.