Exploring Equilibrium Lab

NH₄Cl(g) + Heat ⇌ NH₃(g) + HCl(g)

Objectives: Use an interactive chart and graph to simulate a system in equilibrium and observe how it responds to changes (Le Chatlier's Principle). Then use these observations to determine the equation for a new system in equilibrium (HS-PS1-6)

Exploring Equilibrium 

Imagine you have a seesaw with kids on both sides. If the kids are balanced, the seesaw stays level. This is like chemical equilibrium in a reaction—where the forward and backward reactions happen at the same speed, so the amounts of reactants (starting materials) and products (new substances) stay constant over time. Even though molecules are still changing, the overall amounts don’t appear to change because they are balancing each other out.

However, if something changes—like adding more reactants or increasing the temperature—the "balance" shifts. This is similar to adding more kids to one side of the seesaw, making it tip. The reaction adjusts itself to reach a new balance, following Le Chatelier’s Principle. Just like kids might move around to level the seesaw again, the reaction will shift to counteract the change.

Le Chatelier’s Principle helps us predict how equilibrium shifts when the system is disturbed.

• A shift to the right means the reaction makes more products by using up reactants.
  A shift to the left means the reaction makes more reactants by using up products.
  
  

Interactive Instructions:

In the following interactive, you will experiment with a chemical equilibrium, NH₄Cl(g) + Heat ⇌ NH₃(g) + HCl(g), by adding or removing substances and changing temperature or pressure. When you click "Update Equilibrium", the system will update with the changes you have made, and then adjust to find a new equilibrium. The values will be shown on the graph to the right. as well as updated in the table.

Important Notes:

• Once equilibrium is re-established, the new values become the new starting values for any further changes.

• If a change would result in a negative amount (which is impossible), the system will adjust it to zero instead.
  
  

Your Task:

Investigate how different changes affect equilibrium and record your observations. Complete the CER (Claim-Evidence-Reasoning) prompts on a separate sheet of paper.

Part 1: Exploring Equilibrium Responses to Changes

Part 1 Questions: Use the correct option in parentheses to complete the claim, and then support with evidence and reasoning.

1. C: When you add a substance to one side of the equilibrium, the equilibrium shifts (away from / towards) that side.
   E:
   R:

2. C: When you remove a substance from one side of the equilibrium, the equilibrium shifts (away from / towards) that side.
   E:
   R:

3. C: Things on the same side of the arrow will respond (in the same way/ in different ways) than each other.
   E:
   R:

4. C: Things on opposite sides of the arrow will respond (in the same way / in different ways) than each other.
   E:
   R:

5. C: Increasing pressure shifts the equilibrium (towards / away from) the side with fewer moles of gas.
   E:
   R:

6. C: Increasing the temperature shifts the equilibrium (towards / away from) the side with heat written in it.
   E:
   R:

Part 2: Determining the Equilibrium Equation

You’ve been asked to help a chemist study a newly discovered chemical equilibrium involving three substances: A, B, and X. Your goal is to figure out the balanced equilibrium equation, including the role of heat, by conducting an interactive investigation.

Use your observations from the simulation or lab to determine how each substance and heat factor into the equation.

Your Task:

Write your findings using the C-E-R format (Claim, Evidence, Reasoning):

• Claim: State your proposed equilibrium equation based on your experimental results.
  (Example: A + Heat ⇌ X + B)

• Evidence: Describe what you observed during the experiment.
  (Example: When A was added, B increased and X decreased.)

• Reasoning: Explain how your observations support your proposed equation.
  (Example: Since adding A caused B to increase, B must be on the same side as X, opposite from A.)

Reminders:

• Be specific about how each substance (A, B, and X) behaved when changes were made.

• Don’t forget to explain where heat belongs in the equation (on the reactants or products side).

• Make sure your reasoning clearly connects your evidence to your final equation.

Standards

HS-PS1-6. Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.

SEP

Constructing Explanations and Designing Solutions 

• Apply scientific principles and evidence to provide an explanation of phenomena and solve design problems, taking into account possible unanticipated effects. (HS-PS1-5)

• Refine a solution to a complex real-world problem, based on scientific knowledge, student-generated sources of evidence, prioritized criteria, and trade off considerations. (HS-PS1-6)

CCC

Patterns

• Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena. (HS-PS1-5)

Stability and Change 

• Much of science deals with constructing explanations of how things change and how they remain stable. (HS-PS1-6)