# Worksheet: Reactions on Surfaces

In this worksheet, we will practice describing the effect of surface area on reaction rates, considering how collision frequency scales with surface area.

Q1:

A student is performing a catalytic cracking of liquid paraffin, using porcelain chips as the catalyst. To accelerate the reaction, the surface area of the porcelain chips must be increased. Which of the following tools would be most suitable for this task?

• APestle and mortar
• BCalipers
• CBunsen burner
• DGlass rod
• EIce-water bath

Q2:

Consider a cube with sides that are exactly 10 cm long, as shown: What is the volume of the cube?

What is the surface area of the cube?

If the cube were cut in two, would the total volume and the total surface area increase, decrease, or stay the same?

• AThe total volume would increase and the total surface area would stay the same.
• BThe total volume would stay the same and the surface area would decrease.
• CThe total volume would decrease and the total surface area would increase.
• DThe total volume would stay the same and the total surface area would increase.
• EThe total volume and total surface area would both stay the same.

Q3:

The following combinations of shapes all have the same total volume. Which has the greatest total surface area?

• A • B • C • D Q4:

In a reaction with hydrochloric acid, which of the following forms of calcium carbonate would react most rapidly, assuming the same total mass of calcium carbonate is used?

• AA single sphere
• BA fine powder
• CA cluster of fine needles
• DA single thin plate

Q5:

An insoluble solid is reacted with dilute acid. Why does breaking up the solid into smaller particles increase the rate at which it can react?

• ASplitting the solid into smaller particles increases the kinetic energy of colliding molecules.
• BReducing the particle size of the solid allows more molecules to dissolve and collide with acid molecules.
• CIncreasing the surface area of the solid results in more collisions with acid molecules.
• DBreaking bonds between molecules in the solid liberates bonding electrons to react with acid molecules.
• EWeakening the interactions between molecules in the solid produces gaps to accommodate acid molecules.

Q6:

Dust explosions in flour mills are a serious safety concern. Why is the reaction between the flour particles and the oxygen in the air so fast?

• AThe flour dust acts as a catalyst.
• BThe flour dust has a large surface area resulting in a high collision rate.
• CDust explosions create pressure pockets in the air, increasing the rate of reaction.
• DA dust explosion is exothermic.
• EThe flour dust is highly flammable and concentrated in the air.

Q7:

Which alteration to the conditions of a reaction results in an increase in collision rate and a greater percentage of colliding molecules having sufficient energy to react?

• AIncreasing the pressure
• BIncreasing the surface area
• CIncreasing the concentration
• EIncreasing the temperature

Q8:

In which of the following diagrams will the rate of reaction be slowest?

• A • B • C • D • E Q9:

A pestle and a mortar are often used to produce finer powders from larger lumps of substances such as .

What effect does breaking up a substance in this manner have on the rate of reaction when dilute acid is added to either powdered or larger lumps of ?

• AThe rate of reaction increases as the number of collisions per second increases due to the pressure of the pestle, and the number of particles with sufficient energy to react remains the same.
• BThe rate of reaction increases as the number of collisions per second increases due to the increased concentration, but the number of particles with sufficient energy to react remains the same.
• CThe rate of reaction increases as the number of collisions per second increases due to the increased surface area, but the number of particles with sufficient energy to react remains the same.
• DThe rate of reaction increases as the number of collisions per second increases due to the increased surface area, and the number of particles with sufficient energy to react also increases.
• EThe rate of reaction increases as the number of collisions per second increases due to the increased concentration, and the number of particles with sufficient energy to react also increases.

Q10:

Which of the following factors does not increase the frequency of collisions in a chemical reaction?

• AIncreasing the pressure of reacting gases
• BIncreasing the activation energy
• CIncreasing the temperature
• DIncreasing the surface area of solid reactants
• EIncreasing the concentration of reactants in a solution

Q11:

Polyethene is formed from ethene gas. Which of the following combinations of conditions would lead to the fastest rate of reaction?

• ALow temperature and low pressure
• BHigh temperature and high pressure
• CHigh temperature and low pressure
• DLow temperature and high pressure

Q12:

In experiment 1, excess hydrochloric acid is reacted with a magnesium ribbon weighing 0.5 g in total. In experiment 2, the same experiment is performed with 0.5 g of magnesium powder rather than a ribbon. Which of the following statements describes and explains the differences in the rate of reaction?

• AExperiment 2 has a faster rate of reaction as the magnesium powder is more concentrated.
• BExperiment 1 has a faster rate of reaction as the magnesium ribbon is more concentrated.
• CExperiment 1 has a faster rate of reaction as the magnesium ribbon has a greater surface area.
• DExperiment 1 has a faster rate of reaction as the magnesium ribbon is under more pressure.
• EExperiment 2 has a faster rate of reaction as the magnesium powder has a greater surface area.

Q13:

Solution A is aqueous sodium thiosulfate and solution B is hydrochloric acid. Upon mixing, the given reaction takes place. Which of the following alterations to this experiment would not result in an increase in the rate of reaction?

• AAdding water to solution B
• BCarefully warming solution B
• CDissolving more sodium thiosulfate into solution A
• DIncreasing the temperature of solution A
• EIncreasing the concentration of solution B

Q14:

In which of the following diagrams will the rate of reaction be fastest?

• A • B • C • D • E Q15:

A series of experiments were carried out using uniform pieces of magnesium ribbon and excess hydrochloric acid of varying concentrations. Assuming the proportionality of the rate to the concentration of acid and the number of pieces of magnesium, what are the correct values for , , and ?

Pieces of Magnesium RibbonConcentration of hydrochloric acidTime
160
11.0
21.030
12.0
• A: 2.0
: 30
: 15
• B: 0.5
: 30
: 15
• C: 0.5
: 60
: 30
• D: 0.5
: 30
: 60
• E: 1.0
: 15
: 15