Equilibrium

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# Equilibrium - PowerPoint PPT Presentation

Equilibrium. The state at which the concentrations of all reactant and all products remain constant with time. Equilibrium Position. Indicates if the concentrations of the reactants or the concentration of the products are favored at equilibrium. For the general equation:.

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## PowerPoint Slideshow about 'Equilibrium' - whitby

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### Equilibrium

The state at which the concentrations of all reactant and all products remain constant with time.

Equilibrium Position
• Indicates if the concentrations of the reactants or the concentration of the products are favored at equilibrium.
For the general equation:
• jA + kB  l C +mD
• The equilibrium expression is K = [C]l [D]m
• [A]j [B]k
• Where K is the equilibrium constant
Write the equilibrium expressions for:
• 4NH3 + 7O2 4NO2 + 6H2O
• K = [NO2]4[H2O]6
• [NH3]4[O2]7
• K customarily is written without units.
In general
• The equilibrium expression for a reaction is the reciprocal of that for the reaction written in reverse.
• If a reaction is multiplied by n, the equilibrium expression and K are raised to the nth power.
Carbon Monoxide reacts with steam to produce carbon dioxide and hydrogen. At 700 K the equilibrium constant is 5.10. Calculate the equilibrium concentration of all species if 1.0 mole of each reactant is placed into a 1.0 L flask.
The formation of HF from hydrogen and fluorine gases has an equilibrium constant of 115. Calculate the equilibrium concentration of all species if 3.00 mole of HF is introduced into a 1.5 L container?
Reaction Quotient (Q)
• Q will tell you which way a reaction will proceed if you have both reactants and products present. For the reaction:

N2+ 3H2  2NH3

Q = [NH3]02

[N2]0 [H2]03

If Q = K the system is at equilibrium.
• If Q < K products will form
• If Q > K reactants will form
The formation of HF from H2 and F2 has a K = 115 .
• If 3.00 moles of H2, F2 and HF were introduced into a 1.50 L flask. What would the equilibrium concentrations of all species be?
Equilibria involving pressuresKp
• Partial pressures can be used the same way as concentrations.
• 2NO(g) +Cl2(g)2NOCl(g)
• Kp = PNOCl2
• (PNO)2 (PCl2)
Kp = K (RT)Dn
• R = 0.08206 atm L/K mol
• T = Kelvin temp
• Dn = the sum of the coefficients of the gaseous products – sum of the coefficients of the gaseous reactants.
From the reaction for the formation of nitrosyl chloride(NOCl)
• If at equilibrium
• PNO = 0.050 atm
• PCl2 =0.30 atm
• PNOCl = 1.2 atm
• What is Kp and K for this reaction
Because experimental results show that the position of an equilibrium is not dependant on the amount of pure solids or pure liquids present in a system, they do not appear in the equilibrium expression.
Le Chatelier’s Principle
• If a change is imposed on a system at equilibrium, the position of the equilibrium will shift in the direction that will reduce that change.
Effect of change in concentration
• Add a reactant; shift to products
• Add a product; shift to reactants
• Remove reactant; shift to make more reactants
• Remove product; shift to make more products.
As4O6(s) + 6C(s) As4(g) + 6CO(g)
• Predict the direction of shift of the equilibrium position when:
• Gaseous arsenic is removed.
Effect of change in pressure
• Adding an inert gas; will increase the total pressure of the system but will have no effect on the concentrations or partial pressures of the reactants or products. This will not shift the equilibrium position.
Effect of change in pressureChanging the container volume
• If volume of the container holding a gaseous system is reduced, the system will reduce its own volume. Shift to the side with fewer gas particles
• If volume is increased the system will increase its volume . This will restore the equilibrium pressure.
• P4(s) + 6Cl2(g) 4PCl3(l)
• PCl3(g) + Cl2(g)  PCl5(g)
• PCl3(g) + 3NH3(g) P(NH2)3(g) +

3HCl(g)

Effect of change in temperature
• A change in temperature effects both the equilibrium position and the value of the equilibrium constant.
• The change depends on if the reaction is exothermic or endothermic.
In an endothermic reaction an increase in temperature will result in more products and the value of K will increase.
• In an exothermic reaction an increase in temperature will result in the production of reactants and the value of K will decrease.
Predict the shift in equilibrium position and the change in K if the temperature increases:
• N2(g) + O2(g) +181 kJ  2NO(g)
• 2SO2(g)+O2(g) 2SO3(g)+ 198 kJ