Please answer the following two questions Question: How can you recognize when t

Question

Please answer the following two questions

Question: How can you recognize when the system is at equilibrium?

Question: In a chemical reaction, what corresponds to the addition of more water to the reactant cylinder? How did the final volume of water in the product cylinder change as a result of adding more water to the rectant cylinder?

The Experiment:

The Data:

The graph:

ExpressLab Modelling Equilibrium in this ExpressLab. you will model what happens when forward and reverse reactions occur. You will take measurements to gain quantitative insight into an equilibrium system. Then you will observe the effect of introducing a change to the equilibrium. 7. Add approximately 5 mL of water to the reactant cylinder. Record the volume in each cylinder cylinder:. Record the volume in each cylinder. Then repeat steps 4 and 5 until there is no further change in volume Analysis 1. Plot a graph of the data you collected. Put trans 2 graduated cylinders (25 mL) fer number on the x axis and volume of water on the y-axis. Use different symbols or colours to distinguish between the reactant volume and the product volume. Draw the best smooth curve through the data. 2 glass tubes with different diameters (for example 10 mm and 6 mm) 2 labels or a grease pencil supply of water, coloured with food dye Procedure . Copy the following table into your notebook, to 2. In this activity, the volume of water is a model for concentration. How can you use your graph to compare the rate of the forward reaction with the rate of the reverse reaction? What happens to these rates as the reaction proceeds? record your observations. Transler Votume of water inVolume of water in number reactant cylinder(mL product cylinder (m 3. At the point where the two curves cross, is the rate of the forward reaction equal to the rate of the reverse reaction? Explain. 0 4. How can you recognize when the system is at 2. Label one graduated cylinder "reactant." Label 5. Were the volumes of water (that is, concentra the other "product. tions of reactants and products) in the two tubes equal at equilibrium? How do you know? 3. Fill the reactant cylinder with coloured water, up 6. In a chemical reaction, what corresponds to the to the 25.0 mL mark. Leave the product cylinder empty. addition of more water to the reactant cylinder? How did the final volume of water in the product cylinder change as a result of adding more water to the reactant cylinder? 4. With your partner, transfer water simultaneously from one cylinder to the other as follows: Lower the larger-diameter glass tube into the reactant cylinder. Keep the top of the tube open. When the tube touches the bottom of the cylinder cover the open end with a finger. Then transfer the liquid to the product cylinder. At the same time as you are transferring liquid into the product cylinder, your partner must use the smaller-diameter tube to transfer liquid from the product cylinder into the reactant cylinder 7. Determine the ratio Volume of product at the Volume of reactant end of the first equilibrium and at the end of the second equilibrium. Within experimental error were these two ratios the same or different? 8. In this activity, what do you think determined the relative volumes of water in the graduated cylinders? In a real chemical reaction, what factors might affect the relative concentrations of reactants and products at equilibrium? 5. Remove the glass tubes. Record the volume of water in each graduated cylinder, to the nearest 0.1 mL 9. Explain why the system in this activity is a ciosed system 6. Repeat steps 4 and 5 until there is no further change in the volumes of water in the graduated Chapter 7 Reversible Reactions and Chemical Equilibrium MHR 325

Explanation / Answer

Question: How can you recognize when the system is at equilibrium?
Answer: The Concept of Equilibrium can be summarized as follows:

As a chemical reaction progresses
•   The reactant concentration, [R], decreases to a constant,
•   The product concentration, [P], increases from zero to a constant.
•   When [R] and [P] are constant, equilibrium is achieved.

In terms of rates, the forward reaction rate is high initially and then decreases as reactant molecules are being used up. As the product concentration begins to increase, the reverse reaction rate also increases until the forward and reverse reaction rates are equal and equilibrium is achieved.
At Trial 4 -- reactant volume is 12.5 mL and product volume is 12.2 mL in between 12.2-12.5 equilibrium attained.
The amount of water transferred represented the rate of each of the forward and reverse reactions. The more water taken out of the cylinder with every transfer, the faster the rate. The less water removed with each transfer the slower the rate. This was continued until 3 successive transfers resulted in no further change in volume of water which represented a state of “equilibrium”.

Question:In a chemical reaction, what corresponds to the addition of more water to the reactant cylinder?
Answer: equilibrium shifts towards product side

Question: How did the final volume of water in the product cylinder change as a result of adding more water to the rectant cylinder?
Answer: the final volume of water in the product cylinder increases

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