Section 17.2 Factors Affecting Chemical Equilibrium Describe how various factors affect chemical equilibrium. Explain how Le Châtelier’s principle applies to equilibrium systems. When changes are made to a system at equilibrium, the system shifts to a new equilibrium position. Section 17-2

Le Châtelier’s Principle Le Châtelier’s Principle was proposed in 1888 and states that if stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. Stress is any kind of change in a system that upsets the equilibrium. Section 17-2

Le Châtelier’s Principle (cont.) Adjusting the concentrations of either the reactants or the products puts stress on a system in equilibrium. Adding reactants increases the number of effective collisions between molecules and upsets the equilibrium. Section 17-2

Le Châtelier’s Principle (cont.) The equilibrium shifts to the right to produce more products. Stress is relieved by shifting to the left, converting products to reactants. Section 17-2

What dose the longer equilibrium arrow to the left or right mean? It means that, one reaction occurs faster than the other temporarily. Once a new equilibrium position is established, the two reactions again occur at equal rates

Le Châtelier’s Principle (cont.) Changing the volume (and pressure) of an equilibrium system shifts the equilibrium only if the number of moles of gaseous reactants is different from the moles of gaseous products. CO(g)+ 3H2(g)⇌ CH4(g)+ H2O(g) If the number of moles is the same on both sides of the balanced equation, changes in pressure and volume have no effect on the equilibrium. Section 17-2

Le Châtelier’s Principle (cont.) The reaction between CO and H2 is at equilibrium. Lowering the piston decreases the volume and increases the pressure. As a result, more molecules of the products form. Their formation relieves the stress on the system. Section 17-2

Le Châtelier’s Principle (cont.) Changes in temperature alter the equilibrium position and the equilibrium constant. If heat is added to an equilibrium system, the equilibrium shifts in the direction in which the heat is used up. Section 17-2

Le Châtelier’s Principle (cont.) Any change in temperature results in a change in Keq. Section 17-2

Le Châtelier’s Principle (cont.) A catalyzed reaction reaches equilibrium more quickly, but with no change in the amount of product formed. Section 17-2

A B C D Section 17.2 Assessment Which does NOT result in a shift of the equilibrium to the right? A. removing products B. adding reactants C. increasing concentration of reactants D. adding products A B C D Section 17-2

A B C D Section 17.2 Assessment Any change in ____ results in a change in Keq. A. temperature B. pressure C. volume D. concentration A B C D Section 17-2

A change in ____ alters both the equilibrium position and the equilibrium constant. A. pressure B. temperature C. volume D. density A B C D Chapter Assessment 1

A B C D Adding product to a chemical equilibrium: A. does nothing B. creates a stress and shifts the equilibrium to the right C. creates a stress and shifts the equilibrium to the left D. causes more product to form A B C D STP 3

Ethylene (C2H4) reacts with hydrogen to form ethane (C2H6) Ethylene (C2H4) reacts with hydrogen to form ethane (C2H6). C2H4(g) + H2(g) ↔ C2H6(g) + heat. How could you increase the amount of hydrogen in the system? A. Increase the heat. B. Decrease the heat. C. Increase the C2H4. D. Decrease the C2H6. A B C D STP 4

Which does NOT result in a shift of the equilibrium to the right? A. removing products B. adding reactants C. increasing concentration of reactants D. decreasing the concentration of reactants A B C D STP 5

Q1:why the addition of a catalyst does not change an equilibrium position. A catalyst speeds up the forward and reverse reactions equally. Q2: Explain how the following stresses affect the equilibrium system. PF3(g) + F2(g) ⇌ PF5(g) + heat If volume is decreased: The equilibrium shifts to the right. Heat is increased : The equilibrium shifts to the left.

Q3:Explain how a system at equilibrium responds to a stress and list factors that can be stresses on an equilibrium system. If possible, the equilibrium shifts in the direction that relieves the stress. changes in concentration, pressure (volume), and temperature

Q4:Explain how decreasing the volume of the reaction vessel affects each equilibrium. 2SO(g) + O2(g) ⇌ 2SO(g) H2 (g) + Cl2(g) ⇌ 2HCl(g) a. The equilibrium shifts to the right. b.The stress has no effect on the equilibrium

Q5: Decide whether higher or lower temperatures will produce more CH3CHO in the following equilibrium. C2H2(g) + H2O(g) ⇌ CH3CHO(g) ∆H° = -151 kJ lower temperatures

Q6: The table below shows the concentrations of Substances A and B in two reaction mixtures. A and B react according to the equation 2A ⇌ B; K eq = 200. Are the two mixtures at different equilibrium positions? The two mixtures are at the same equilibrium position.

End of section 17.2