1. The problem statement, all variables and given/known data What is the effect on the system below which is already at equilibrium if extra hydrogen was added? How is the amount of I2 different? 2. Relevant equations 2HI ⇔ H2 + I2 3. The attempt at a solution I am finding effects the addition or removal of a substance at chemical equilibrium not making a lot of sense. To me it's contradicting, especially when you refer to graphs. For example the solution to this would be: the system tries to oppose this change by removing this extra Hydrogen. It does this by favouring the reverse reaction, thus equilibrium shifts to the left, and there is now more Hydrogen Iodide than previous. The amountof I2 has decreased as it has been used to react with the extra H2 to form HI. What i don't understand is how equilibrium constant doesn't change. How is this possible? If you have more HI and less I2, mathematical the concentration fraction will be less. This is observed on many equilibrium vs time graphs with adding or removing substances. It clearly does show a differing Kc value if you added all the concnetrations.