The principle
Disturb a system at equilibrium and it responds in the direction that partly undoes the disturbance.
Concentration
Adding any species pushes Q away from K in that species' direction, and the shift consumes what you added
K never moves. Only Q does, so the mixture returns to the same K
Temperature
Endothermic (ΔH > 0): heating raises K and favours products
Exothermic (ΔH < 0): heating lowers K and favours reactants
Only temperature changes K. Everything else just moves Q
Volume and pressure
Compressing raises every concentration, so Q scales by V−Δn and the shift heads toward fewer gas moles
Δn(gas) = 0 means Q is untouched by the piston, so nothing shifts
Inert gas at fixed volume changes no concentration, so it changes nothing
This system
N₂O₄ ⇌ 2 NO₂Nitrogen dioxide dimer. The sealed-tube demo. Warm it brown, chill it colourless.
ΔH° = +57.2 kJ/mol · Kc(298 K) = 6.10×10⁻³ · Δn(gas) = +1