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Understanding Chemical Equilibrium: States, Principles, and Impacts on Reactions

This chapter explores the various states of a chemical system: dynamic change, static systems, and equilibrium. It presents the concept of equilibrium in reversible reactions, where the rate of the forward process equals the rate of the reverse. Key topics include the equilibrium constant (K_eq), the reaction quotient, and Le Chatelier’s Principle, which details how systems respond to changes in pressure, concentration, and temperature. Examples, practice problems, and questions enhance comprehension of these fundamental concepts in chemical equilibrium.

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Understanding Chemical Equilibrium: States, Principles, and Impacts on Reactions

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  1. Chapter 16 Chemical Equilibrium

  2. Different States a System Can Be In • A state of change • No change (there are several no change states

  3. 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

  4. 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.

  5. 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

  6. 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)

  7. Reaction Quotient • The reaction quotient is the same mathematical expression as Keq only it is taken when the system is not at equilibrium.

  8. 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.

  9. 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.

  10. 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.

  11. 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)

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