Module 3 - Chemical Equilibrium
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What does dynamic equilibrium mean?
It occurs when the rate of forward reaction equals the rate of reverse reaction and the concentration of reactants and products remain constant in a closed system
Changing what factors can alter the position of equilibrium?
● Concentration of reactants or products ● Pressure ● temperature
Explain the 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) ΔH°= +210 kJ mol -1 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.)
In the equation: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ΔH°= +210 kJ mol-1 What effect would increasing the pressure have on the position of equilibrium?
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). Therefore the yield of hydrogen decreases.
The reaction: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ΔH°= +210 kJ mol-1 Suggest and explain why an industrial chemist may use a high pressure for this production of hydrogen from the above reaction?
The high pressure increases the collision frequency thus 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]^2 / [A]^2[B]^3[C]
Deduce units for the value of kc= [D][E]^2 / [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 or 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 of an endothermic reaction have on Kc ?
Kc decreases
What effect does increasing the temperature of an endothermic reaction have on Kc ?
Kc increases
What effect does decreasing the temperature of an exothermic reaction have on Kc ?
Kc increases
What effect does increasing the temperature of an exothermic reaction have on Kc ?
Kc decreases