4. a) i. Define phase equilibrium. [2 marks] ii. Name 3 phase transformation processes. [3 marks] b) Coalbed methane extraction is done by drilling a gas well to the coalbed and then pump out the ground water to release the trapped methane. The released methane not only goes up to the well but also seep through any opening to water well source that are around the methane extraction side. Methane at elevated concentration in water can escape quickly causing an explosive hazard in poorly ventilated or confined areas. Consider a water well at 25C and exposed to atmosphere. Assuming the space above the water level consists of a saturated mixture of methane and water vapor. Calculate: i. the mole fraction of the water vapor in the saturated mixture. [4 marks] ii. the mass fraction of dissolved methane in the water. [16 marks]