Chemical Equilibria 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)
ΔH°= +210 kJ mol-1
The equilibrium position shifts to the left.
This is because the forward reaction is produces more moles of gas than the reverse reaction (4 moles of product, 2 moles of reactant). 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)
ΔH°= +210 kJ mol-1
- 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?
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
mol-1 dm3
What does Kc being greater or lesser than 1 suggest for the position of equilibrium?
> 1 = over to the right
<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
What effect does increasing the temperature in an exothermic reaction have on Kc?
Kc decreases
