Changes in concentration

• If all other conditions stay the same, the equilibrium constant?K_c?is?not affected?by any changes in concentration of the reactants or products
• For example, the decomposition of hydrogen iodide:

2HI ? H₂?+ I₂

The equilibrium expression is:

Adding more HI makes the ratio of [ products ] to [ reactants ] smaller

To restore equilibrium, [H₂] and [I₂] increases and [HI] decreases

Equilibrium is restored when the ratio is 6.25 x 10^-3?again

Changes in pressure

• A change in pressure?only?changes the?position?of the equilibrium?(see Le Chatelier’s principle)
• If all other conditions stay the same, the equilibrium constant?K_c?is?not affected?by any changes in pressure of the reactants and products

Changes in temperature

• Changes in temperature?change?the equilibrium constant?K_c
• For an endothermic reaction such as:

An increase in temperature:

[H₂] and [I₂]?increases

[HI]?decreasesBecause [H₂] and [I₂] are?increasing?and [HI] is?decreasing, the equilibrium constant?K_c?increases

• For an exothermic reaction such as:

An increase in temperature:

[SO₃]?decreases

[SO₂] and [O₂]?increasesBecause [SO₃]?decreases?and [SO₂] and [O₂]?increases?the equilibrium constant?K_c decrease

Presence of a catalyst

• If all other conditions stay the same, the equilibrium constant?K_c?is?not affected?by the presence of a catalyst
• A catalyst speeds up both the forward and reverse reactions at the same rate so the ratio of [ products ] to [ reactants ] remains unchanged

Answer:

• • Only a change in temperature will affect the value of?K_c?and any other changes in conditions would result in the position of the equilibrium moving in such way to oppose this change.
  • Adding a catalyst will increase the rate of reaction meaning the state of equilibrium will be reached faster but will have no effect on the position of the equilibrium and therefore?K_c?is unchanged.