Question

Explain about Andrew’s experimental isotherms of CO₂ gas.

Answer 1

1. Andrew plotted isotherms of carbon dioxide at different temperatures. it is then proved that many real gases behave in a similar manner like CO₂ .

2. At a temperature of 303.98 K, CO₂ remains as a gas. Below this temperature, CO₂ , turns into liquid CO₂ at 73 atm. It is called the critical temperature of CO₂ .

3. At 303.98 K and 73 atm pressure, CO₃,, becomes a liquid but remains a gas at higher temperature.

4. Below the critical temperature, the behaviour of CO₂ is different. 

For example, consider an isotherm of CO₂ at 294.5 K, it is a gas until the point B, is reached. At B, a liquid separates along the line BC, both the liquid and gas co-exist. At C, the gas is completely condensed.

5. If the pressure is higher than at C, only the liquid is compressed so, a steep rise in pressure is observed. 

Thus, there exist a continuity of state.

6. A gas below the critical temperature can be liquefied by applying pressures.