Please complete this exit quiz.

This quiz will test your understanding of the topic Reversible Reactions.

A reversible reaction can reach equilibrium. In a closed system, equilibrium is reached when the forward and reverse reaction happen at the same ___________

Which of the following can escape from a 'closed system'?

Photosynthesis is a process that takes in light energy to convert water and carbon dioxide into glucose and oxygen. Photosynthesis is an _________________ reaction.

What does the symbol ⇌ mean?

When ammonium chloride is heated, it breaks down to form ammonia and hydrogen chloride. What needs to be done to turn ammonia and hydrogen chloride back to the original reactant - ammonium chloride?

Reversible Reactions

﻿Hello, everyone. I hope you're all doing great. It's me, Dr. Dang. And welcome back to Chemistry. As we are heading towards the end of this unit, The Rate and Extent of Chemical Change. In this lesson, you're going to learn about an important principle in chemistry, Le Chatelier's principle. This is one of my favourite topics in chemistry, which is applied in many industries when it comes to manufacturing chemical products. So before we begin, please find yourself a quiet space, where you can sit and work through this lesson free from any distractions, turn off the notifications on your mobile phone, or switch it off completely because can, close down all browser tabs that are not being used so you can make the most of this lesson. So when you're ready, let's get started. We are going to start the lesson by going over dynamic equilibrium. This is extremely important in order for us to understand Le Chatelier's principle, then we would look at who Le Chatelier is, and the idea behind Le Chatelier's principle. Next, we were focused on the effect of changing concentration and temperature on the position of equilibrium in a chemical reaction using Le Chatelier's principle. And finally, at the end of the lesson, you're going to do a quiz and practise a couple of exam style questions to consolidate your learning. In terms of the equipment that you need for this lesson, you will only need a writing pen and some paper or something to write on. If you do not have any of these with you right now, please take a moment and pause lesson to go and collect your equipment, then resume once you're ready. Great. So let's start by answering this question. So get ready because I have a task for you. What is dynamic equilibrium? Pause lesson now to answer this question, then resume when you have an answer. Wonderful. Let's take a look at what dynamic equilibrium is. An equilibrium is the point in a reaction when the forward and reverse reactions occur at exactly the same rate in a closed system. We looked at this definition in a previous lesson, and I mentioned the importance of learning what equilibrium means. You must include the key terms that I've underlined in this definition when you're explaining equilibrium. So in the example on the screen, equilibrium is achieved when the rate of the forward reaction where A and B react together to form C and D is exactly the same as the rate at which C and D react together to form A and B. So this brings me onto my next question. What is a closed system? Pause the lesson now to answer this question, then resume once you're finished. Okay. So how many of you remembered what a closed system is? Let's go over this. A closed system is where neither the reactants or products can enter or leave and dynamic equilibrium can only be achieved in a closed system. Now let's move on and take a look at who Le Chatelier is, and the idea behind Le Chatelier's principle. Le Chatelier's principle was proposed by a French chemist called Henry Louis Le Chatelier. It is an extremely important principle in chemistry, especially when it comes to chemical processing. As this is used to predict how changing conditions affect the position of equilibrium and ultimately the yield of the product, which is the mass of a product made from a chemical reaction. So we will be using Le Chatelier's principle to determine the effect of changing different conditions such as concentration, temperature and pressure on the position of equilibrium and the yield. Le Chatelier's principle States that, if a system is at equilibrium and a change is made to any of the conditions including concentration, temperature, and pressure, the system will respond to counteract the change. For example, if you heat up the system, it will respond to cool down. And likewise, if you cool the reaction, the system will respond to heat up. So let's take a look at the effect of changing concentration on the position of equilibrium using Le Clatelier's principle. When we work with a reaction that involves solutions, increasing the concentration of a solute will shift the equilibrium in the direction away from this solute. This is the system's way of counteracting that change when the concentration of one of the substances is increased. Let's take a look at this example here. What happens to the equilibrium if we increase the concentration of A? We know that A is one of the reactants that will react with B to form products, C and D in the forward reaction. And by increasing the concentration of A, they equilibrium will shift in the direction that is away from A. So we say equilibrium shifts to the rights away from A in the reaction, therefore increasing the concentration of C. Before we move on and look at another question, I would like us to watch a video together, which is used to demonstrate the shift of an equilibrium in a reaction. This is a video showing the blue bottle experiment, which is often used to explain equilibrium. So let's watch the together, and make sure you're listening carefully.

In the flask I have some distilled water. I'm going to add some glucose to the water. I'm going to swirl this and have the glucose dissolve. Glucose is a sugar. Glucose reacts with the oxygen in the air slowly to produce carbon dioxide and water. If I add some potassium hydroxide, the potassium hydroxide acts as a catalyst to speed up the rate at which the glucose reacts with the oxygen in the air. I'm going to add a few drops of an indicator called Methylene Blue. Methylene Blue is blue in the presence of oxygen and is colourless in the absence of oxygen. I'm going to swirl the flask and let it stand for a few minutes. I'm going to swirl the flask again, and let it stand. Swirl the flask, and let it stand. Explain what's happening in the flask.

In this blue bottle experiment, What did you notice about the colour of the solution when the person shakes the bottle? That's right, we notice by shaking the bottle, the solution goes from colourless to blue. And this is because when we shake the bottle, the concentration of the oxygen that is saturated increases, therefore shifting the equilibrium to counteract this change. Which is why the solution turns colour colourless again, after a while, as it is less standing still. All right, now let's take a look at another question. So looking at this reaction, what do you think will happen to the equilibrium if we increase the concentration of B? Remember in our answer, we must mention the direction in which the equilibrium shifts to. So you can either say that it shifts in the forward direction or the reverse direction. You can also say it shifts to the left or shifts to the right. So what is it going to be? So in this reaction, B is on the reactant side. So by increasing the concentration of B, the equilibrium is going to shift away from B. So which direction is that? Equilibrium shifts to the right, away from B in the equation and this will increase the concentration of C. Now, I would like you to answer this next question on your own. Pause the lesson here to answer this question on your piece of paper, then resume once you have completed this task. Well done. Now let's take a look at the answer. So by increasing the concentration of C, equilibrium shifts to the left away from C, and this is going to decrease the concentration of C. So now let's take a look at the effect of changing temperature on the position of equilibrium using Le Chatelier's principle. Remember when we learned about reversible reactions, we said that, if a reaction is exothermic in one direction, it must be endothermic in the opposite direction. So you must bear this in mind when we look at the effects of changing temperature on the position of equilibrium. So what does Le Clatelier's principle tell us? If the temperature is increased, the position of the equilibrium shifts in the direction of the endothermic process. And an endothermic reaction will have an overall energy change that is a positive value, because energy is taken in from the surroundings, and the change in H tells us the overall energy change. So in other words, increasing temperature favours endothermic. Please take a moment to write this down so you can refer back to this in case you forget. Pause the lesson now to do this then resume once you're ready. Great. So what do we think will happen to the position of equilibrium when we decrease temperature? Good. So it's going to be the opposite. If the temperature is decreased, the position of the equilibrium shifts in the direction of the exothermic process. And an exothermic reaction will have an overall energy change that is a negative value, because energy is transferred to the surroundings. So in other words, decreasing temperature favours exothermic. Once again, please take a moment to write this down. So pause the lesson now to do so. Excellent. Now let's apply this to a couple of examples. First example, the forward reaction is endothermic. Explain what happens to the equilibrium and yield if we increase the temperature of the reaction. So don't forget, in your answer you need to mention the direction in which the equilibrium is going to shift, and you must mention what is going to happen to the yield. So the yield being the mass of the desired product. So when we increase temperature, which reaction does this favour? Endothermic or exothermic? You can check in notes if you need to. That's right. So increasing temperature favours endothermic. So in this case, that is the forward reaction. Therefore equilibrium shifts to the right, and we need to explain this by saying, increasing temperature, favours, endothermic reaction and this is going to increase the yield. And we know this because the equilibrium is going to shift to the right in the forward direction towards the yield. Let's take a look at another example where the question is turned around slightly. The forward reaction is endothermic. Explain what happens to the equilibrium and yield if we decrease the temperature of the reaction? The forward reaction is endothermic. So by decreasing the temperature, which reaction does that favour? You can check your notes. That's right. Decreasing temperature, favours exothermic. Therefore equilibrium shifts to the left. And we can explain this by saying decreasing temperature Favours exothermic reaction, and this is going decrease the yield. So don't forget if the equilibrium is going to shift to the left away from whether yield is, then less yield is going to be produced. Okay. Now I would like you to try answering this next question on your own. So here's your question. Read it carefully. Pause lesson now to try it, then resume once you're finished. Well done. Now let's check your answer. So in this question, the forward reaction is exothermic. What happens to the equilibrium and yield when temperature is increased? So remember increasing temperature favours? That right. Increasing temperature favours the endothermic reaction. So therefore, equilibrium shifts to the left. And we can explain this by saying increasing temperature, favours endothermic reaction, which is the reverse direction, and this is going to decrease the yield. So well done if you've got this right. Now, I would like you to try just one more question on your own. So here you have the same reaction, read the question carefully. Pause the lesson now to answer this question, then resume once you've completed this task. Excellent. Now let's check your answer. In this question the forward reaction is exothermic. So what can we do to the temperature to increase the yield? So we need to start by thinking in which direction does the equilibrium need to shift in order to increase the yield? That's right. So that will be in the forward direction or we can say to the right. And the foreign reaction is exothermic and therefore decreasing temperature favours exothermic reaction in the forward direction. So in other words, this reaction over here favours a low temperature and a massive well done if you answered this correctly. Okay. So before we move on to practise a couple of exam style questions, let's do a quick quiz to check that you've understood what we've just gone through. These are going to be quick-fire multiple choice questions. I will read the questions out and you will get a good couple of seconds to choose the right answer. So are you ready? Let's go then. Which of the following condition or conditions can be changed in the system that is in equilibrium? And in three, two, one, the answer is D. All of the above. Next question. In a reaction, what will happen to the equilibrium if the concentration of one, the reactants is increased? And in three, two, one, the answer is D. It shifts to the right. Next question. In a reaction involving solutions, if the concentration of a solute is increased in which direction will equilibrium shift to? And in three, two, one, the answer is C. It's going to shift away from the solute. Next question. In our reaction that is endothermic in the forward reaction, what will happen to the equilibrium if the temperature is increased? And in three, two, one, the answer is B. They equilibrium will shift to the right, because don't forget, increasing temperature favours endothermic. Next question. In a reaction that is exothermic in the forward reaction what will happen to the yield if the temperature is increased? And in three, two, one, the answer is D. The yield will decrease, because increasing temperature favours endothermic, therefore the equilibrium is going to shift to the left. Or in other words, it's going to shift away from where the yield is, and this is going to decrease the yield. Well done if you answered all of these questions correctly. Now, I would like you to practise a couple of exam style questions independently. So when the questions show up on your screen, please pause lesson and write down your answers on your sheets of paper, then resume once you have finished. Here is exam style question one. Please pause lesson now to complete this task, then resume once you're finished. Great. Now let's take a look at exam style question two. Here's question two. Please pause lesson now to complete this task, then resume once you're finished. Excellent. Now let's go through the answers, so be prepared to assess your work. There are the answers for exam style question one. Pause the lesson, again to check your work, then resume once you're finished. Great. Let's move on then. There are the answers for exam style question two. Pause the lesson again to assess your work, then resume once you're finished. Fantastic. And well done if you answered most of these questions correctly. Great. Now let's summarise what we've covered in this lesson. At the beginning, we went over the definition for dynamic equilibrium and a closed system. Then we looked at who Le Chatelier is, and the idea behind Le Clatelier's principle. Next, we learned about the effect of changing concentration and temperature on the position of equilibrium using Le Chatelier's principle. And finally, we did a quiz to check your understanding, and you also had the opportunity to practise a couple of exam style questions independently. We have now arrived at the end of the lesson. There are downloadable resources available, and don't forget to complete the exit quiz so know how well you've been listening in this lesson. I hope you found this lesson interesting, and I look forward to seeing you in our next lesson, where we will look at the effect of changing pressure on the position of equilibrium using Le Clatelier's principle. Thank you for joining me and I will see you soon. Bye.

Please complete this exit quiz.

This quiz will test your understanding of the topic - Le Chatelier's Principle: Effect of Changing Concentration and Temperature

A reversible reaction is exothermic in the forward reaction, the reverse reaction is... ?

Increasing temperature favours...

In a reaction that is exothermic in the forward direction, what happens to equilibrium when temperature is increased?

In a reaction involving solutions, if the concentration of a solute is decreased, in which direction will equilibrium shift to?

Which of the following is the state symbol for a solution?

In a closed system, equilibrium is the point in the reaction where the forward and reverse reactions are occurring at exactly the same ____________ ?

Le Chatelier's Principle: Effect of Changing Concentration and Temperature

State and apply Le Chatelier's principle to any reversible reaction

Describe the effect on equilibrium of changes to temperature and concentration

Choose and explain the conditions needed to achieve a high yield

In this lesson, higher tier students will learn to interpret appropriate given data to predict the effect of a change in concentration and temperature of a reactant or product on given reactions at equilibrium.

Chemistry

Y11 Chemistry

Key Stage 4

Year 11

Le Chatelier's principle: Effect of changing concentration and temperature

The rate and extent of chemical change

UNIT

Rate of reaction

Rate of reaction using graphs and tangents

Collision theory

Planning an investigation to find rate of reaction

Rate of reaction required practical (Part 1)

Rate of reaction required practical (Part 2)

Effect of changing surface area on rate of reaction

Effect of changing temperature on rate of reaction

Effect of changing pressure on rate of reaction

Catalysts

Reversible reactions

Le Chatelier's principle: Effect of changing pressure

Le Chatelier's principle: Uses in industry

The Rate and extent of chemical change: Review (Part 1)

The Rate and extent of chemical change: Review (Part 2)

For a reversible reaction that is exothermic in the forward direction, what effect does increasing temperature have on the position of equilibrium?

In the Haber process, an iron catalyst is used to speed up the rate of reaction. What effect does adding a catalyst have on the position of equilibrium?

In a reaction that involves gases, increasing the pressure will shift the equilibrium to...

Hypothesis: Increasing the concentration of hydrochloric acid increases the rate of reaction when reacting with magnesium. What is the independent variable (variable that is being changed)?

Hypothesis: Increasing the concentration of hydrochloric acid increases the rate of reaction when reacting with magnesium. What is the dependent variable (variable that is being measured)?

Hypothesis: Increasing the concentration of hydrochloric acid increases the rate of reaction when reacting with magnesium. Which of the following are the control variables? (Tick THREE)

How can we check reproducibility to ensure the data obtained from a practical is of high quality?

Which of the following marble chips has the largest surface area to volume ratio?

Calcium carbonate (marble chips) react with hydrochloric acid to produce calcium chloride, water and what gas?

Calculate the mean rate of reaction when 23 cm³ of gas is produced in 15 seconds.

What happens to the volume of gas when pressure is increased?

What happens to the reacting particles when pressure is increased?

Why does the rate of reaction increase when pressure of reacting gases increases?

Which of the following equipment can we use to collect and measure volume of gas? Tick TWO boxes.

What is the gas produced when magnesium reacts with hydrochloric acid?

Increasing the concentration of reactants in a solution will result in...

What does the gradient of a graph tell us if the x axis is time and y axis is volume of gas collected?

Lesson overview:Le Chatelier's principle: Effect of changing concentration and temperature

The rate and extent of chemical change: