Advanced Chemical Principles and Molecular Dynamics · 6th Year

Active learning ideas

Reversible Reactions and Dynamic Equilibrium

Challenge your students to look beyond reactions that go to completion. This topic introduces the fascinating, two-way nature of reversible reactions and the concept of dynamic equilibrium.

• NCCA Curriculum Specifications
• Leaving Certificate Chemistry Syllabus: Physical Chemistry - Chemical Equilibrium

• 15–25 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Simulation Game
• 20 min · Small Groups

The Cobalt Chloride Colour Shift

Students observe a solution of cobalt(II) chloride. Adding concentrated HCl shifts the equilibrium to form the blue [CoCl₄]²⁻ complex, while adding water shifts it back to the pink [Co(H₂O)₆]²⁺ complex, visually demonstrating a reversible reaction.

Explain the meaning of the term 'dynamic equilibrium'.

Facilitation Tip

Ensure good ventilation as concentrated HCl is used; a teacher demonstration is a safe alternative.

What to look for

Use mini-whiteboards for students to predict the direction of equilibrium shift (left, right, or no change) when a specific stress is applied to a given reaction.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Activity 02

• Simulation Game
• 15 min · Pairs

Beads in Beakers Equilibrium Model

In pairs, students transfer beads between two beakers using different sized scoops to represent forward and reverse reaction rates. They continue until the 'concentration' (number of beads) in each beaker remains constant, modelling dynamic equilibrium.

Identify the conditions necessary for a system to reach equilibrium.

Facilitation Tip

Encourage students to graph the number of beads in each beaker over time to visualise the approach to equilibrium.

What to look for

A multi-part Leaving Cert-style exam question on the Haber process, requiring students to state Le Châtelier's principle, explain the choice of industrial conditions, and describe the equilibrium involved.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Activity 03

• Simulation Game
• 25 min · Individual

Haber Process Decision Making

Using a worksheet or simple simulation, students act as chemical engineers. They must choose the optimal temperature and pressure conditions for ammonia production, justifying their choices using Le Châtelier's principle and considering the trade-off between reaction rate and yield.

Compare the macroscopic and microscopic properties of a system at equilibrium.

Facilitation Tip

Prompt students to also consider the economic costs associated with high pressure and low temperature.

What to look for

Provide students with a RAG (Red, Amber, Green) rating sheet with the key learning objectives, allowing them to self-evaluate their confidence in each area.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

A few notes on teaching this unit

Begin with a concrete physical analogy, like the 'Beads in Beakers' model, to establish the concept of a dynamic balance. Then, use a striking visual demonstration, such as the cobalt chloride reaction, to bridge the analogy to a real chemical system. Finally, apply these foundational ideas to the abstract and industrially significant Haber process.

Upon completing these activities, students will be able to apply Le Châtelier's principle to predict how real chemical systems, from a test tube to an industrial reactor, respond to change.

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Watch Out for These Misconceptions

• At equilibrium, the reactions have stopped.

  Equilibrium is dynamic. Both the forward and reverse reactions are still occurring, but their rates are equal, so there is no net change in the concentrations of reactants and products.

• Equilibrium means there are equal amounts of reactants and products.

  The concentrations of reactants and products are constant at equilibrium, but they are rarely equal. The position of equilibrium determines the relative amounts of each.

• A catalyst changes the position of equilibrium to favour the products.

  A catalyst increases the rate of both the forward and reverse reactions equally. It allows the system to reach equilibrium faster but does not change the final equilibrium position or the yield of products.

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Methods used in this brief

• Simulation Game