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Different States a System Can Be In • A state of change • No change (there are several no change states
No Change States • static system – no movement, no change (example: a rock in a jar) • steady state system – is a flow through system with no net change, is an open system (example: the earth and the flow of energy from the sun to the earth and then into outer space) • equilibrium – the forward process is equal to the reverse process so there is no net change, is a closed system
Equilibrium examples • a reversible chemical reaction • 2NO2(g) ↔ N2O4(g) • The forward and reverse reactions are taking place at the same time. • When the rate of the forward reaction is equal to the rate of the reverse reaction, the system is at equilibrium.
The law of Chemical Equilibrium • Every reversible reaction proceeds to an equilibrium state. • Regardless of how much of each chemical you start with the system will shift so that concentrations of the products divided by the concentrations of the reactants will always be a constant. • Do sample problem page 543 • Assign practice problems 1 & 2 on page 543
Equilibrium constant is Keq • If Keq 1 the products are favored. • Keq 1 the reactants are favored. • The concentrations of the pure solids or liquids can be left out of the formula – Their concentration does not change and becomes part of the Keq. • Do sample problem 2 on page 545 • Assign practice problems 3 & 4 on page 545 (write Keq and give the equation)
Reaction Quotient • The reaction quotient is the same mathematical expression as Keq only it is taken when the system is not at equilibrium.
Le Chatelier’s Principle (leh-shaht-lee-ay) • When pressure (stress) is placed on a system the system will shift to relieve the pressure (stress). • Increasing the pressure will favor the side that requires less volume. • 2NO2(g) ↔ N2O4(g) • Changing the pressure will change the equilibrium constant.
Adding a compound to an equilibrium • This will “push” the reaction to favor the other side of the equation. • 2NO2(g) ↔ N2O4(g) • This will remove some of the compound that has been added. • This does not change the equilibrium constant.
Removing a compound • 2NO2(g) ↔ N2O4(g) • This will cause the equilibrium to shift to favor (make more of) the material that is being removed. • This does not change the equilibrium constant.
Effects of changing Temperature • H2 + I2↔ 2HI + heat • Adding heat will drive the reaction to the left. • Removing heat (cooling) pulls the reaction to the right. • This will change the equilibrium constant • Chapter questions page 558-559 (1 - 14, 17, 18, 20, 21, 23, 24, 26, 27, 28, 29)