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The apparatus shown below was used to investigate the rate of formation of hydrogen gas according to the following balanced equation - Leaving Cert Chemistry - Question 9 - 2022
Question 9
The apparatus shown below was used to investigate the rate of formation of hydrogen gas according to the following balanced equation. Zn + 2HCl → ZnCl2 + H2 The re... show full transcript
Worked Solution & Example Answer:The apparatus shown below was used to investigate the rate of formation of hydrogen gas according to the following balanced equation - Leaving Cert Chemistry - Question 9 - 2022
Step 1
What is meant by the rate of a chemical reaction?
Answer
The rate of a chemical reaction is defined as the change in concentration of a reactant or product per unit time. Typically, it can be measured by the amount of reactant consumed or product formed over a specific time period. A faster reaction will have a higher rate, indicating more rapid change.
Step 2
Plot a graph (on graph paper) of volume of H2 versus time (x-axis).
Answer
To create the graph, plot the time (in minutes) on the x-axis against the volume of hydrogen gas (in cm³) on the y-axis. Each pair of data points from the table will correspond to a point on the graph. Connect these points to visualize the trend.
Step 3
Does the rate of this reaction increase or decrease with time?
Answer
The rate of this reaction decreases with time. Initially, as zinc is added to the hydrochloric acid, the reaction occurs rapidly, producing hydrogen gas. However, as time progresses and the reactants are consumed, the frequency of effective collisions decreases, leading to a slower reaction rate.
Step 4
Step 5
Step 6
From your graph find (iii) the average rate of the reaction over the first 5 minutes (in cm³ of H2 per minute at room temperature).
Answer
To calculate the average rate of reaction over the first 5 minutes, use the formula: ext{Average Rate} = rac{ ext{Change in Volume}}{ ext{Time Interval}} For the first 5 minutes, the volume increased from 0 cm³ to approximately 60 cm³, so: ext{Average Rate} = rac{60 - 0}{5 - 0} = 12 ext{ cm³/min}
Step 7
How would you expect the initial rate of this reaction to be affected by (i) using the same volume of a more concentrated HCl solution?
Answer
Using a more concentrated HCl solution would increase the initial rate of the reaction. A higher concentration of hydrochloric acid increases the number of acid particles in the same volume, leading to a higher frequency of collisions with zinc pellets, thus accelerating the reaction rate.
Step 8
How would you expect the initial rate of this reaction to be affected by (ii) using the same mass of powdered zinc instead of the pellets of zinc?
Answer
Using powdered zinc instead of zinc pellets would also increase the initial rate of reaction. The increased surface area of powdered zinc allows for more collisions with hydrochloric acid molecules, facilitating a faster reaction compared to using larger zinc pellets.