Chemical Equilibria, Le Chatelier’s principle and Kc Flashcards
Define the term dynamic equilibrium.
The rate of the forward reaction is equal to the rate of the reverse reaction.
Give an essential condition for an equilibrium mixture.
Equilibrium occurs in a closed system (where
reactants and products cannot escape)
State Le Chatelier’s principle.
If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance.
What effect would increasing the temperature have on the position of
equilibrium? In the equation: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ΔH°= +210 kJ mol-1
The equilibrium position shifts to the right.
This is because the forward reaction is endothermic. Yield of hydrogen increases.
What effect would increasing the pressure have on the position of equilibrium? In the equation: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)
The equilibrium position shifts to the left.
This is because the forward reaction is produces more moles of gas than the
reverse reaction.
Yield of hydrogen
decreases.
Suggest and explain why an industrial chemist may use a high pressure for the production of hydrogen from: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)
The high pressure increases the collision frequency, increasing the rate of reaction.
This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen.
What effect does a catalyst have on the position of equilibrium?
No effect because catalyst affects rate of forward and reverse reactions equally
What condition affects the value of Kc? ❑ Concentration ❑ Catalyst ❑ Pressure ❑ Temperature
temperature
For the reaction below, deduce an expression for Kc
2[A] + 3[B] + [C] ⇌ [D]+4[E]
Kc=[D][E]4/[A]2[B]3[C]
Deduce units for the value of Kc
Kc=[D][E]4/[A]2[B]3[C]
mol-1 dm-3
What type of system is Kc relevant for?
Homogeneous systems in equilibrium
What does Kc being greater/less than 1 suggest for the position of equilibrium?
Greater than 1 = over to the right
Less than 1 = over to the left
What effect does decreasing the temperature in an endothermic reaction have on Kc ?
Kc decreases
What effect does increasing the
temperature in an endothermic reaction have on Kc ?
Kc increases
What effect does decreasing the
temperature in an exothermic reaction have on Kc ?
Kc increases
