The formation of a gas is a clue to chemical changes. The bubbles of gas that you observed form when an antacid is dropped into water is an example of change. ... As wood burns, it turns into a pile of ashes and gases that rise into air.
In a reaction at equilibrium in which reactants and products are gases, pressure is a factor that produces a shift of the equilibrium position. When the pressure is increased, the equilibrium is shifted to the side of the reaction with a fewer moles. In this reaction:
2 HD(g) ⇀↽ H₂(g) + D₂(g)
There is the same number of moles on both sides:
reactants side: 2 moles HD
products side: 1 mol H₂ + 1 mol D₂ = 2 moles
Therefore, the equilibrium position will not change.
