Chemical Equilibria - Physical 1 Flashcards
Define the term dynamic equilibrium.
The rate of the forward reaction is equal to the rate of the reverse reaction.
(Hence, the concentrations of reactant and product do not change)
Give an essential condition for an equilibrium mixture.
● Equilibrium occurs in a closed system (where reactants and products cannot escape)
OR
● Macroscopic properties do not change with time
State Le Chatelier’s principle.
If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance.
In the equation:
CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) -1
ΔH°= +210 kJ mol
What effect would increasing the temperature have on the position of equilibrium?
The equilibrium position shifts to the right.
(This is because the forward reaction is endothermic. Yield of hydrogen increases.)
The reaction:
CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) -1
mol
ΔH°= +210 kJ
Suggest and explain why an industrial chemist may use a high pressure for this production of hydrogen from the above reaction?
1.
The high pressure increases the collision frequency, increasing the rate of reaction.
2.
This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen.
In the equation:
CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) -1
ΔH°= +210 kJ mol
What effect would increasing the pressure have on the position of equilibrium?
⇌ CO
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.
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
❑ Concentration
❑ Catalyst
❑ Pressure
❑ Temperature
For the reaction below, deduce an expression for Kc .
2[A] + 3[B] + [C] ⇌ [D]+ 4[E]
[D][E]4
————— = Kc
[A]2[B]3[C]
what are the units for the value of Kc for:
[D][E]4
————— = Kc
[A]2[B]3[C]
mol-1 dm3
What effect does increasing the temperature in an endothermic reaction have on Kc ?
Kc increases
What type of system is Kc relevant for?
Homogeneous systems in equilibrium
What does Kc being greater of lesser than 1 suggest for the position of equilibrium?
Greater than 1 = over to the right Lesser than 1 = over to the left
What effect does decreasing the temperature in an endothermic reaction have on Kc ?
Kc decreases
What effect does decreasing the temperature in an exothermic reaction have on Kc ?
Kc increases
