State and explain the andrews experiment for liquification of gases
Answers
Liquefaction of Gases
FacebookTwitterGoogle+WhatsApp
Gases are difficult to transport. Due to their physical properties, it is almost impossible to transfer them from one place to another. For the same purpose, the gas is transformed into a liquid. Study of liquefaction of gases tells us about changes in the properties and structure of a gas. It also gives valuable information about the structure of matter in general. Let’s see how.
Liquefaction
Liquefaction is the transformation of a gaseous substance into its liquid state. This change is the outcome of change in physical conditions like temperature, pressure, and volume. Thomas Andrew was the first person to study the change of state from gases to liquids in Carbon Dioxide. It was later discovered that most real gases behave like Carbon Dioxide (CO2) and change from gases to liquids if optimum physical changes in temperature and pressure are achieved.
In his experiment on CO2, Andrews came to a conclusion that at high temperatures, despite high pressure, the gases cannot be liquefied. Also with the increase in temperature, the gases show significant deviation from the ideal behavior. In the case of carbon dioxide, at 30.98° C, the gas started changing into a liquid.
Critical Temperature, Volume, and Pressure
Andrews in his experiment observed that above a specific temperature, the gas sample couldn’t be liquefied, howsoever high the pressure becomes.The critical temperature is the temperature at which a gas changes into liquid. With the increase in temperature, the pressure required to liquefy a gas also increases. This temperature was the highest temperature at which a gas appears in the form of a liquid. It is the critical temperature or TC.
Critical constants play an essential role in the change of states of matter. Critical constants are critical pressure, temperature, and volume. The volume of one mole of a gas volume liquefied at critical temperature is known as the critical volume (Vc) while the pressure required to liquefy the gas at critical temperature is called as the Critical pressure (pc).
Isotherm of Carbon Dioxide
The graph between the Pressure and Volume at a given constant temperature is the isotherm. On studying the isotherm of Carbon dioxide we get to know the different intervals of temperatures at which a gas can show signs of liquefaction:
Liquefaction of Carbon Dioxide
On studying the isotherm above we get to know the physical change of state temperature wise. Volume and pressure play a vital role in the change of state. In the above isotherm, we study the liquefaction of Carbon dioxide.
We see that the gaseous state of carbon dioxide changes to liquid at 30.98° C. The curve changes at a lower temperature, while at the higher temperature it does not show any change. At 30.98°C, the gas shows considerable deviation from the ideal gas behavior.
Equilibrium state
Here we notice that the curve at increased pressure signifies compressibility of liquid CO2 while the steep line pertains to the isotherm of the liquid, slightest of compression results in a sharp rise in the pressure, thus indicating the amount of compressibility of CO2. On attaining 21.5° Carbon dioxide behaves like a gas until point B.
The point B shows signs of liquid CO2 . The gas now exists in the dual form i.e both liquid and gas. At this stage compressing further does not affect the pressure on the gas, rather it results in condensation. At point C, all the CO2 gas has condensed and further compression results in the rise in pressure.
From the above isotherm it is clear that at point A, CO2 exists in the gaseous state while at point D it exists in a liquid state. At point D the compression of the liquid CO2 is almost impossible. At point C an equilibrium state between the two states of matter is seen.
We further find that the behavior of all the gases is similar to CO2 and this is because of the constant temperature or isothermal compression. This similar behavior shown by gases, in compression, at constant temperature is known as isothermal compression.
Gases to liquids
The critical temperature of the gas is the highest temperature at which the first occurrence of liquefaction of gas is seen.The critical temperature signifies the force of attraction between the molecules.The higher the critical temperature, higher is the intermolecular force of attraction and easier is the liquefaction of the gas.
Gases require cooling and compression both for liquefaction.