Equilibrium
Definition
Equilibrium refers to the state in which both reactants and products are present in concentrations which have no further tendency to change over time. It's when forward and reverse reactions occur at equal rates so there's no net change observed.
Analogy
Imagine you're on a see-saw with your friend who weighs exactly as much as you do. When you're both sitting still at an equal height off ground level - neither going up nor down - that's equilibrium!
Related terms
Dynamic Equilibrium: A state of balance between continuing processes.
Le Chatelier's Principle: This principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change.
Equilibrium Constant (K): The ratio of concentrations of products to reactants at equilibrium, each raised to a power equal to its stoichiometric coefficient in the balanced chemical equation.
"Equilibrium" appears in:
Study guides (14)
AP Chemistry - 5.1 Reaction Rates
AP Chemistry - 5.9 Steady-State Approximation
AP Chemistry - 7.1 Introduction to Equilibrium
AP Chemistry - 7.2 Direction of Reversible Reactions
AP Chemistry - 7.7 Calculating Equilibrium Concentrations
AP Chemistry - 7.8 Representations of Equilibrium
AP Chemistry - 7.10 Reaction Quotient and Le Châtelier’s Principle
AP Chemistry - 7.12 Common Ion Effect
AP Chemistry - 8.2 pH and pOH of Strong Acids and Bases
AP Chemistry - 8.3 Weak Acid and Base Equilibria
AP Chemistry - 8.4 Acid-Base Reactions and Buffers
AP Chemistry - 8.8 Properties of Buffers
AP Chemistry - 9.5 Free Energy and Equilibrium
AP Chemistry - 9.9 Cell Potential Under Nonstandard Conditions
Practice Questions (20+)
- A reaction between nitrogen and hydrogen to create ammonia is found to be exothermic at equilibrium. The reaction is then placed into an oven. Which of the following statements is true?
- A reaction vessel contains some amount of calcium carbonate and calcium oxide, and the system is found to be at equilibrium. If carbon dioxide is injected into the vessel, which of the following is true?
- Equilibrium is established in a reaction vessel, of which argon (Ar) is not a reactant nor product. What happens when argon (Ar) is added to a reaction vessel AT CONSTANT VOLUME?
- Equilibrium is established in a reaction vessel, of which argon (Ar) is not a reactant nor product. What happens when argon (Ar) is added to a reaction vessel AT CONSTANT PRESSURE?
- Consider the equation N₂ (g)+ 3H₂ (g) ⇌ 2NH₃ (g). The ΔH° is -92.6 kJ/mol. Which of the following statements about concentration after the adjusted equilibrium is NOT true?
- Consider the equation 2SO₃ ⇌ O₂ + 2SO₂. Given a K value of 8 and concentration of 2M for all substances, which way must the reaction move to reach equilibrium?
- What are the rates of forward and reverse reactions at equilibrium?
- A + 3B ⇌ 2C + 2D is at equilibrium. The initial concentration of A is 1.2 M, and the initial concentration of B is 1.5 M. The concentration of C at equilibrium is 0.6 M. What is the equilibrium constant, K?
- At equilibrium, which of the following is true?
- What is the thermodynamic definition of equilibrium in AP Chemistry?
- Which of the following statements is true about the relationship between free energy and equilibrium?
- The cell potential is a driving force toward equilibrium; the farther the reaction is from equilibrium, the ____ the magnitude of the cell potential.
- In general terms, equilibrium is defined as the point at which the rate of the reaction is ________ is similar to the reaction __________ and the concentrations _____________.
- Wen at equilibrium, the forward and backward rate _______________________.
- Let's clear up a common misconception! Is equilibrium a dynamic process?
- A reaction vessel is filled such that the concentration of hydrogen gas, chlorine gas, and hydrogen chloride each have a partial pressure of 1.0 atm. What happens to the total pressure of the reaction vessel as the reaction proceeds to equilibrium?
- Consider the reaction N2(g) + O2(g) ⇌ 2NO(g). If the reaction is at equilibrium and the pressure is increased, what is the effect on the direction of the reaction?
- Consider the reaction 2H2(g) + S2(g) ⇌ 2H2S(g). If the concentration of H2S is increased, what is the effect on the direction of the reaction at equilibrium?
- What is the value of Kp given that at equilibrium, the partial pressure of oxygen gas is 2.0 atm, the partial pressure of a free oxygen atom is 1.0 atm, and the partial pressure of ozone is 4.0 atm at 298 K?
- A reaction is shown to occur and has reached equilibrium, with all molecules being in a gaseous state. A+2B+C⇌3D is the reaction and it happens at 298 K in a closed container with a defined volume. The partial pressure of the molecules is shown below. What is the equilibrium expression Kp for this reaction? PA = 0.50 atm PB = 0.02 atm PC = 1.50 atm PD =0.05 atm
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