Question

why do we lower the temperature while liquefing the gas

Answer 1

We know the condensation process
in which vapour turns into water droplets by lowering the temperature. In the same way we have to decrease temp. in order to liquefy a gas.

Answer 2

We know the condensation process
in which vapour turns into water droplets by lowering the temperature. In the same way we have to decrease temp. in order to liquefy a gas.