Sec 4 Chemistry Rate of Reactions topical questions

State the meaning of the term rate of reaction and name one quantity that can be measured to follow the rate of a reaction between marble chips and dilute hydrochloric acid.

State the effect on the rate of reaction of each change, for a reaction between a solid and a solution.

1. (a)Increasing the concentration of the solution[1]
2. (b)Grinding the solid into a powder[1]
3. (c)Lowering the temperature[1]

A student collects 36 cm³ of gas in the first 3.0 minutes of a reaction. Calculate the average rate of gas production.

Name the substance recovered unchanged at the end of a reaction that lowers the activation energy, and write the equation for the decomposition of hydrogen peroxide that it catalyses.

List four factors that change the rate of a reaction between a solid and a solution, and give the collision-theory reason for each.

1. (a)Name the four factors.[2]
2. (b)Give the collision-theory reason for any two of them.[2]

24 cm³ of carbon dioxide is collected in 40 seconds.

1. (a)Calculate the average rate in cm³/s.[2]
2. (b)State how the instantaneous rate near the end would compare.[1]

Explain, using collision theory, why dilute hydrochloric acid reacts faster with magnesium powder than with magnesium ribbon of the same mass.

Explain why a 10 °C rise in temperature can roughly double the rate of a reaction.

Equal masses of calcium carbonate are reacted with excess dilute hydrochloric acid, once as large chips and once as powder. Both reactions are run at room temperature and both syringes end at 48 cm³ of CO₂.

1. (a)Sketch-in-words the two volume–time curves on the same axes.[2]
2. (b)Explain why the curves start differently.[1]
3. (c)Explain why both curves finish at the same volume.[2]

A student times how long a cross under a beaker takes to disappear as sodium thiosulfate reacts with hydrochloric acid, repeating the experiment at different temperatures.

1. (a)Name the yellow-white solid causing the cloudiness.[1]
2. (b)State and explain what happens to the time as the temperature rises.[2]
3. (c)State one safety precaution for this experiment.[2]

On a graph of hydrogen volume against time for zinc and sulfuric acid, the curve is steepest at the start and gradually flattens, plateauing after 6 minutes.

1. (a)Explain why the curve is steepest at the start.[2]
2. (b)Explain why the curve flattens.[2]
3. (c)State what the plateau value represents.[1]

Excess marble chips react with dilute hydrochloric acid and the carbon dioxide volume is recorded.

1. (a)Calculate the average rate between 0 and 10 s.[1]
2. (b)Calculate the average rate between 40 and 60 s.[1]
3. (c)Explain why the two rates differ.[2]

A student plans to investigate how temperature affects the rate of reaction between magnesium ribbon and dilute hydrochloric acid, using a gas syringe.

1. (a)Describe how the investigation is carried out at two temperatures.[3]
2. (b)State two variables that must be controlled.[2]

Hydrogen peroxide decomposes slowly on its own: 2H₂O₂ → 2H₂O + O₂. A few grams of manganese(IV) oxide powder are added.

1. (a)State the effect on the rate and on the final volume of oxygen.[2]
2. (b)Explain how the catalyst works.[2]
3. (c)Describe how the catalyst is recovered at the end.[1]

0.24 g of magnesium ribbon (Mr = 24) is added to excess dilute hydrochloric acid and the hydrogen collected in a gas syringe.

1. (a)Calculate the moles of magnesium used.[1]
2. (b)Calculate the volume of hydrogen expected at r.t.p. (24 dm³ per mole).[3]
3. (c)State where the syringe reading will plateau, and what would happen to the plateau if 0.48 g were used instead.[2]

A pharmaceutical plant runs a reaction in solution at 25 °C with a yield of 70%. An engineer suggests heating to 60 °C and adding a catalyst.

1. (a)State and explain the effect of each change on the rate.[3]
2. (b)State the effect of each change on the position of completion (the final amount of product), with a reason.[2]
3. (c)Suggest one reason the plant might NOT want the higher temperature.[1]

Two experiments react identical zinc granules with 50 cm³ of hydrochloric acid. Experiment 1 uses 1.0 mol/dm³ acid at 20 °C; experiment 2 uses 2.0 mol/dm³ acid at 20 °C.

1. (a)Predict which experiment finishes first, with a collision-theory reason.[2]
2. (b)Sketch-in-words both volume–time curves, stating the relationship between the two plateau volumes. Assume the acid is in excess in both runs.[2]
3. (c)State how the curves would change if both experiments were repeated with zinc powder.[2]

0.12 g of magnesium ribbon (Mr = 24) is dropped into excess 1.0 mol/dm³ hydrochloric acid at 25 °C and the hydrogen volume is recorded.

1. (a)Calculate the volume of hydrogen expected when all the magnesium has reacted (r.t.p., 24 dm³/mol).[2]
2. (b)Calculate the average rate between 0 and 20 s and between 80 and 120 s.[2]
3. (c)Explain the change in rate using collision theory.[2]