1. Modelling equilibrium and Le Chatelier’s principle using food dye and water

Using food dye and water is a great way for students to visualise the formation of a dynamic equilibrium. Start with two large containers (or beakers) and label one as reactants and the other as products. In the lab using beakers is great as it is easy to measure the amount of reactants and products being transferred each ‘round’. At home you could use small measuring cups or measuring jugs. 

If you prefer to watch a video then the following video will demonstrate the model I am about to explain. 

Method overview 

Fill each of the containers with the same amount of water and colour each with different colours of food dye. Only add a couple of drops of food dye as you want to be able to observe the colour changes which is easier when they aren’t too dark. Also make sure you use colours that are easy to see a colour change. I like red and blue to make purple, but blue and yellow to make green would also work well.

Then choose two smaller containers of different sizes. Choose one that will represent the rate of the forward reaction, and the other will represent the rate of the reverse reaction.  

Each round you are going to fill the ‘forward’ container with the reactants and then tip it into the products container. Then fill the ‘reverse’ container with the products and tip it into the reactants container. Repeat the rounds until you feel you have observed equilibrium – that is, when the rate of the forward and reverse reaction are equal. You can check this by measuring the liquid or just by sight. This is also a good opportunity to discuss observations about the colour of the system and limitations of the model.

Other alternatives to try:

• Starting with different amounts of reactants and products:
• More reactants than products
• More products than reactants
• All reactants and no products (just a drop of food colouring)
• Changing the size of containers for the reactants and products:
• Same size
• Reactants larger
• Products larger 
• Disturb the equilibrium by adding more reactant in and repeating.

2. Modelling formation of equilibrium using chocolate

If you’re looking for peak engagement in the classroom then look no further than the chocolate aisle! This activity will help students understand equilibrium reactions and also help them to demonstrate an equilibrium reaction on a graph. 

NOTE: Be careful with food allergies and ensure you follow your school’s protocols for food in the classroom. If you are unable to use chocolate or lollies for this activity, counters or paper is a good alternative.

Get a student friendly printable version here 

Method overview

For this activity fold an A4 piece of paper in half and write reactants on one side and products on the other. 

Count out 60 m&ms and place them all on the reactants side of the paper. Decide on a rate for the forward and reverse reactions. For example, the rate of the forward reaction as 0.25 and the reverse reaction as 0.5. For each round transfer the amount of m&ms from one side to the other. So, round #1 you would transfer a quarter of the reactant m&ms to the product side. Since there are currently no products, none would be transferred back to the reactants.

Round #2 you would again transfer a quarter of the reactant m&ms and a half of the product m&ms back again. Repeat rounds until you reach equilibrium (where the number of m&ms being transferred each time is equal).

Have students graph their results by using a different coloured pen for the reactants and products. Help them to identify on their graph where equilibrium was established. 

Other alternatives to try:

• Starting with different amounts of reactants and products:
  • Same amounts of reactants and products
  • More reactants than products
  • More products than reactants
• Changing the ‘rate’ of the forward and reverse reactions:
  • Same rate (same ratio of m&ms transferred each time e.g. 0.5 for both)
  • Reactants faster rate

3. Modelling equilibrium and Le Chatelier’s principle using chocolate

This is my favourite one! I have found that students struggle most when trying to interpret graphs that show multiple disturbances to equilibrium. This activity is a great introduction to these as it helps them to create their own graph that depicts a disturbance that they initiated. 

Get a student friendly printable version here 

Method overview

Start using the exact same activity as above until equilibrium has been established and remained constant for three rounds. Then count out another 20 m&ms. Add these to the reactants side of the page. 

Note: When recording the number of reactants and products for each round ensure the addition of the extra m&ms is added to the last round so that on the graph a vertical line would be drawn. 

Students continue with the same rate of reaction as before and continue until a new equilibrium is reached. 

Other alternatives to try:

• Adding different numbers of m&ms for the disturbance
• Adding m&ms to the product side
• Removing m&ms from the reactant side
• Removing m&ms from the product side

Modelling equilibrium & Le Chatelier’s principle experiments

(suitable for in a laboratory)

Chemistry is a difficult subject to teach as it involves understanding what happens at a molecular level. This is often difficult as we are asking students to understand what they cannot see. 

These experiments assist students in developing their understanding by allowing them to observe disturbances in equilibrium and the formation of a new equilibrium. 

If you are teaching online or don’t have access to a laboratory then check out my video here! In this video I demonstrate each of the following reactions so students can observe them.

Disclaimer: You are responsible for following your own school’s laboratory safety rules and guidelines including which chemicals your students are able to use in the classroom. You may decide to use these as demonstrations. The Animated Teacher is not responsible for any outcome or injury acquired from doing these experiments. 

4. Shifting equilibrium by changing temperature: Nitrogen dioxide to dinitrogen tetroxide

Nitrogen dioxide gas forms an equilibrium in a closed system with dinitrogen tetroxide. The nitrogen dioxide molecules react to form dinitrogen tetroxide at the same rate that the dinitrogen tetroxide decomposes into nitrogen dioxide. 

Nitrogen dioxide is a brown gas while the dinitrogen tetroxide is a colourless gas. When equilibrium is established the system will be a light brown colour due to the combination of both molecules being present. The differing colours in the gases make them excellent for modelling equilibrium and Le Chatelier’s principle as we can see the colour change throughout the process. 

To make the nitrogen dioxide gas, add concentrated nitric acid to pieces of copper metal in a conical flask. Collect the gas in 3 sealable tubes of the same size. NOTE: make sure this is done in a fume cupboard as nitrogen dioxide gas is highly toxic when inhaled.

In this demonstration we can stress the system by changing the temperature of the vessel and therefore observe a shift in equilibrium. We can do this by adding one of the tubes to a hot water bath, one to a cold water bath, and keeping one at room temperature for comparison.

Another alternative is using the reaction between cobalt chloride with hydrochloric acid. This reaction also allows for a clear example of modelling equilibrium and Le Chatelier’s principle due to the varying colours of the reactants and products.

Similarly to above, by putting the system in a hot water bath and a cold water bath, a colour change will be observed showing the shifting of equilibrium.

5. Shifting equilibrium by changing pressure: Nitrogen dioxide to dinitrogen tetroxide

Using the same method as above create nitrogen dioxide and collect in a syringe. Seal the end really well with blutac. NOTE: This experiment should also be performed in a fume cupboard.

2NO2(g) ⇋ N2O4(g)

Once the system has reached equilibrium increase the pressure on the system by compressing the syringe. Leave for a few minutes to allow for the system to reach equilibrium again. 

With an increase in pressure, the system will shift to the side with less moles of gas. In this instance, to the right. Since it shifts to create more dinitrogen tetroxide, the colour should decrease. 

Then decrease the pressure on the system by increasing the volume of the syringe. Again leave for a few minutes for the system to reach equilibrium again. 

With a decrease in pressure, the system will shift to the side with more moles of gas in order to counteract the stress. Therefore, in this system, it will shift to the left to create more nitrogen dioxide. Hence, you should expect to see an increase in the brown colour as nitrogen dioxide is a brown gas.

Now it’s time to disturb it! Shake the flask! This causes more oxygen to dissolve into the solution and oxidise the indigo carmine. The more it is shaken the more oxidised the indicator becomes. If you then leave it to settle you will see the colours change back as equilibrium is established again. 

Conclusion

Modelling equilibrium and Le Chatelier’s principle is so worthwhile in helping students really understand the concepts. Using fun activities that involve chocolate is always a win! 

Have you tried any of these? Let me know how it went in the comments below!

Visit my store to access my resources related to Le Chatelier’s principle here.