← Chemistry syllabus

United StatesChemistry

Unit 7: Equilibrium

14 dot points across 14 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do we calculate the equilibrium concentrations of all species from initial concentrations and the value of K?

Topic 7.7 Calculating Equilibrium Concentrations: use an ICE table and the value of K to calculate equilibrium concentrations, including the use of the small-x (5%) approximation where valid.
A focused answer to AP Chemistry Topic 7.7, covering using an ICE table with a known K to solve for equilibrium concentrations, setting up and solving the resulting equation, and the small-x approximation, with full worked examples.
11 min answer →

How do we calculate the value of an equilibrium constant from equilibrium concentrations or from initial data using an ICE table?

Topic 7.4 Calculating the Equilibrium Constant: calculate the value of an equilibrium constant from equilibrium concentrations or pressures, using an ICE table where initial and equilibrium data are mixed.
A focused answer to AP Chemistry Topic 7.4, covering calculating Kc or Kp from equilibrium values, the ICE table method, and converting between initial and equilibrium concentrations, with full worked examples.
11 min answer →

Why does the solubility of a salt decrease when a common ion is already present in solution?

Topic 7.12 Common-Ion Effect: explain and calculate the reduced solubility of a salt in a solution that already contains one of its ions, using Le Chatelier's principle and Ksp.
A focused answer to AP Chemistry Topic 7.12, covering the common-ion effect, why a shared ion lowers solubility, and how to calculate the reduced molar solubility using an ICE table and Ksp, with full worked examples.
10 min answer →

How do the relative rates of the forward and reverse reactions determine the direction a reversible reaction proceeds?

Topic 7.2 Direction of Reversible Reactions: relate the direction of a reversible reaction to the relative magnitudes of the forward and reverse rates as the system approaches equilibrium.
A focused answer to AP Chemistry Topic 7.2, covering how the relative forward and reverse rates set the net direction of a reversible reaction, the approach to equilibrium from either side, and the connection to rate laws, with full worked examples.
9 min answer →

How does the free energy of dissolution relate to whether and how much a salt dissolves?

Topic 7.14 Free Energy of Dissolution: relate the thermodynamic favourability of dissolving a salt to the enthalpy and entropy of dissolution and to the sign of the free energy change.
A focused answer to AP Chemistry Topic 7.14, covering the enthalpy and entropy of dissolution, how their balance sets the free energy of dissolution, and how the sign of the free energy change relates to solubility, with full worked examples.
10 min answer →

What does it mean for a reaction to reach dynamic equilibrium, and what is happening at the particle level?

Topic 7.1 Introduction to Equilibrium: describe dynamic equilibrium as the state in which the forward and reverse reaction rates are equal and concentrations are constant, at the particle level.
A focused answer to AP Chemistry Topic 7.1, covering dynamic equilibrium, the equality of forward and reverse rates, constant concentrations, and the particle-level picture of a reversible reaction, with full worked examples.
9 min answer →

How does a system at equilibrium respond to a change in concentration, pressure or temperature?

Topic 7.9 Introduction to Le Chatelier's Principle: predict the direction a system at equilibrium shifts in response to a change in concentration, volume or pressure, or temperature, using Le Chatelier's principle.
A focused answer to AP Chemistry Topic 7.9, covering Le Chatelier's principle and how an equilibrium shifts in response to changes in concentration, volume or pressure, and temperature, including the effect on K of temperature, with full worked examples.
11 min answer →

How does the solubility product constant describe the equilibrium of a slightly soluble salt, and how is it used?

Topic 7.11 Introduction to Solubility Equilibria: write the solubility product expression Ksp for a slightly soluble salt and relate Ksp to molar solubility and ion concentrations.
A focused answer to AP Chemistry Topic 7.11, covering the solubility product constant Ksp, writing the Ksp expression, relating Ksp to molar solubility, and using Q versus Ksp to predict precipitation, with full worked examples.
11 min answer →

What does the magnitude of an equilibrium constant tell us about the extent of a reaction?

Topic 7.5 Magnitude of the Equilibrium Constant: interpret the size of an equilibrium constant as a measure of the extent of reaction, relating large, small and intermediate K to the dominant species at equilibrium.
A focused answer to AP Chemistry Topic 7.5, covering how the size of the equilibrium constant indicates whether products or reactants dominate at equilibrium, what a very large or very small K means, and the intermediate case, with full worked examples.
9 min answer →

Why does the solubility of certain salts depend on the pH of the solution?

Topic 7.13 pH and Solubility: explain why the solubility of salts of weak acids or bases depends on pH, using Le Chatelier's principle applied to the dissolution and acid-base equilibria.
A focused answer to AP Chemistry Topic 7.13, covering how pH affects the solubility of salts containing basic anions (such as hydroxides, carbonates and fluorides), using Le Chatelier's principle on the coupled dissolution and acid-base equilibria, with full worked examples.
10 min answer →

How does the equilibrium constant change when a reaction is reversed, scaled or added to another reaction?

Topic 7.6 Properties of the Equilibrium Constant: determine how K changes when a reaction is reversed (reciprocal), scaled (power) or combined with another reaction (product), and relate Kc to Kp.
A focused answer to AP Chemistry Topic 7.6, covering how the equilibrium constant transforms when a reaction is reversed, multiplied by a factor or added to another reaction, and the relationship between Kc and Kp, with full worked examples.
10 min answer →

How are the reaction quotient and the equilibrium constant defined, and how do they predict the direction of reaction?

Topic 7.3 Reaction Quotient and Equilibrium Constant: write the expression for the reaction quotient Q and the equilibrium constant K, and compare Q with K to predict the direction of reaction.
A focused answer to AP Chemistry Topic 7.3, covering the reaction quotient Q, the equilibrium constant K, the law of mass action, Kc and Kp, and comparing Q with K to predict the direction a reaction will shift, with full worked examples.
11 min answer →

How does comparing the reaction quotient with K explain the direction of a Le Chatelier shift?

Topic 7.10 Reaction Quotient and Le Chatelier's Principle: explain the direction of an equilibrium shift quantitatively by comparing the reaction quotient Q with K after a disturbance.
A focused answer to AP Chemistry Topic 7.10, covering how a disturbance changes Q relative to K, why the system shifts to restore Q equals K, and how this gives a quantitative explanation of Le Chatelier's principle, with full worked examples.
10 min answer →

How can particulate diagrams and graphs represent a system at equilibrium and the relative amounts of species?

Topic 7.8 Representations of Equilibrium: interpret and construct particulate diagrams and concentration-versus-time graphs that represent a system at equilibrium and the relative amounts of reactants and products.
A focused answer to AP Chemistry Topic 7.8, covering particulate (particle) diagrams of equilibrium mixtures, concentration-versus-time graphs, relating the relative amounts to the equilibrium constant, and identifying when equilibrium is reached, with full worked examples.
9 min answer →