• Changes in temperature?change?the equilibrium constants?Kc?and?Kp
• For an endothermic reaction such as:

???An increase in temperature:

???[H2] and [I2]?increases

???[HI]?decreases

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

• For an exothermic reaction such as:

???An increase in temperature:

???[SO3]?decreases

???[SO2] and [O2]?increases

???Because [SO3]?decreases?and [SO2] and [O2]?increases?the equilibrium constant??decreases

Answer

• • Only temperature changes permanently affect the value of?Kp
  • An increase in temperature shifts the reaction in favour of the products.
  • The [ products ] increases and [ reactants ] decreases, therefore, the?Kp?value increases.

• How the equilibrium shifts with temperature changes:

Effect on the value of the equilibrium constant

• For a reaction that is exothermic in the forward direction, increasing the temperature pushes the equilibrium from right to left
• Therefore, the value of?the equilibrium constant?will decrease as the ratio of [ products ] to [ reactants ] decreases
• Conversely, if the temperature is raised in an endothermic reaction, the value of?the equilibrium constant?will increase

• If all other conditions stay the same, the equilibrium constant?Kc?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
• If all other conditions stay the same, the equilibrium constant?Kc?is?not affected?by any changes in pressure of the reactants and products
• The value of?Kp?is not affected by any changes in pressure.
• Changes in pressure cause a shift in the position of equilibrium to a new position which restores the value of?Kp
• This is analogous to what happens to?Kc?when you change concentration in an aqueous equilibrium; a shift restores equilibrium to a new position maintaining?Kc

Presence of a catalyst

• If all other conditions stay the same, the equilibrium constants?Kp?and?Kc?are?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
• Catalysts only cause a reaction to reach equilibrium?faster
• Catalysts therefore have?no effect?on the?position of the equilibrium?once this is reached