What sank the Kursk?

Controlling the rate of reaction

HCCHEMISTRY

HCCHEMISTRY

After completing this topic you should be able to :

Controlling the rate of reaction

HCCHEMISTRY

HCCHEMISTRY

• understand that the rate of some reactions can be increased using a catalyst

• Learn how a catalyst speeds up reaction rate by lowering the activation energy, and how to represent this on a potential energy diagram.

• Devise an experimental investigation into the decomposition of hydrogen peroxide.

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K-141 Kursk was an Oscar-II class nuclear-powered cruise missile submarine of the Russian Navy, lost with all hands when it sank in the Barents Sea on 12 August 2000. Kursk, full name Атомная подводная лодка «Курск», which, translated, means the nuclear-powered submarine "Kursk" [АПЛ "Курск"] in Russian, was a Project 949A Антей (Antey, Antaeus, also known by its NATO reporting name of Oscar II). It was named after the Russian city Kursk, around which the largest tank battle in history, the Battle of Kursk, took place in 1943 (world war 2). One of the first vessels completed after the end of the Soviet Union, it was commissioned into the Russian Navy's Northern Fleet.

Starter Activity

• Pupils to work in groups (2-4)• Pupils to be given the News timeline and Arces Worksheet • Issue a mini whiteboard to each group and ask them to write

down what information they can deduce from the table and timeline.

Many points arise here but they should include that the sinking of the Kursk involved hydrogen peroxide.There were two explosions at roughly the same place in quick succession, the second more powerful than the first.

Pose questions to highlight that the decomposition:• has been accelerated by the presence of a catalyst• occurs at a sufficiently high temperature to vaporise

the water• proceeds at a very fast rate, rather like an explosion.

Hydrogen Peroxide Demonstration

(emphasize to pupils that ours is not HTP High-test peroxide or HTP is a high (85 to 98 percent)-concentration solution of hydrogen peroxide, with the remainder predominantly made up of water. In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with no remaining liquid water. It was used as a propellant of HTP rockets and torpedoes, and has been used for high-performance vernie engines.)

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Potential energy graphs and catalysts

P.E.

50 -

25 -

Reaction path

75 -

60 -

Reactants

Products

Uncatalysed

Catalysed

Potential energy graphs and catalysts

Catalysts lower the activation energy needed for a successful collision.

Activation energy Ea for the forward uncatalysed reaction

P.E.

Reactants

Products

Reaction path

Activation energy Eafor the forward catalysed reaction

50 -

25 -

75 -

60 -

Potential energy graphs and catalysts

Catalysts lower the activation energy needed for a successful collision.

Activation energy Ea for the reverse uncatalysed reaction reaction

P.E.

Reactants

Products

Reaction path

Activation energy Ea for the reverse catalysed reaction

50 -

25 -

75 -

60 -

Potential energy graphs and catalysts

P.E.

50 -

25 -

Reaction path

75 -

60 -

∆H Activation energy

Effect of catalyst – forward reaction No change Lowered

Effect of catalyst – reverse reaction No change Lowered

Catalysts lower the activation energy needed for a successful collision.

Reactants

Products

CatalystsA catalyst speeds up the reaction by lowering the activation energy.

A catalyst does not effect the enthalpy change for a reaction

A catalyst speeds up the reaction in both directions and therefore does not alter the position of equilibrium or the yield of product, but does decrease the time taken to reach equilibrium.

Energy distribution and catalysts

Total number of collisions (area underthe graph) with sufficient K.E. energy to create new products.

Catalysed reactionEa is reduced

No ofCollisionswith a givenK.E.

Kinetic energy

Ea

Ea

Un-catalysed reaction

Explain that they are to plan an experiment to compare how effective different powders are in catalysing the decomposition of hydrogen peroxide.• Take the students through the equipment and materials that are available.• Give each student a What sank the Kursk? Worksheet and an Apparatus list.• Ask them to draw a diagram of their apparatus for when they begin their

experiment.• After a suitable time, give out copies of the Apparatus diagram, showing the

expected apparatus.• Pose questions to make explicit why that apparatus has been chosen.• Ask the students to compare their diagram with the one they have been

given.• Get them to write down an experimental procedure based on the Apparatus

diagram they have been given (and which someone else could follow).• After a suitable time give out copies of the Procedure sheet detailing the

expected procedure.• Pose questions to highlight why the procedure has been chosen.• Ask students to compare their experimental procedure with that on

the Procedure sheet.

Apparatus list The equipment available to investigate the effect of different powders on the decomposition of hydrogen peroxide  • Trough• 50 m3 burette which will be inverted • 250 cm3 conical flask with bung fitted• About 75 cm3 of 20 volume hydrogen peroxide per test (Irritant)• Range of powders to test• Small test-tube• Rubber tubing to connect side arm of flask to bottom of upturned

burette• Boss, clamp and stand• Stop clock• Cotton thread• Funnel• 100 cm3 measuring cylinder• Balance weighing to 0.01 g• Eye protection.

Time/ s

Burette reading

/ cm3

Time/ s

Burette reading

/ cm3

Time/ s

Burette reading

/ cm3

20   120   220 40   140   240 60   160   260 80   180   280 100 200   300

Procedure to investigate how powders effect the rate of decomposition of hydrogen peroxide•Half fill a trough with water.•Fill a burette with water, cover the open end with your thumb and upturn so the end is below the surface of the water.•Clamp the burette using a clamp, boss and stand.•Measure 75 cm3 of 20 volume hydrogen peroxide with a measuring cylinder and pour into a conical flask.•Connect the side arm of the flask to the bottom of the burette with rubber tubing.•Weigh out between 0.3 and 0.5 g of powder and put this into the small test-tube.•Tie one end of thread around the test-tube and suspend it above the hydrogen peroxide in the flask.•Simultaneously loosen the bung to drop the test-tube into the flask and start the stop clock.•Record the level of water in the burette every 20 seconds for 5 minutes or until the water level goes below the level of the burette.

Concentrated solutions of hydrogen peroxide are used in the propulsion systems of torpedoes. Hydrogen peroxide decomposes naturally to form water and oxygen:

2H2O2(aq) → 2H2O(ℓ) + O2(g) ΔH = −196∙4 kJ mol–1

Transition metal oxides act as catalysts in the decomposition of the hydrogen peroxide.

Unfortunately, there are hazards associated with the use of hydrogen peroxide as a fuel in torpedoes. It is possible that a leak of hydrogen peroxide solution from a rusty torpedo may trigger an explosion.

Using your knowledge of chemistry, comment on why this could happen.

Discuss with pupils in groups expectations of open-ended questions and their responses.

An official investigation after most of the wreck was raised along with analysis of pieces of debris concluded that a faulty weld in the casing of the practice torpedo caused high-test peroxide (HTP) to leak, which caused the kerosene fuel to explode. The initial explosion destroyed the torpedo room, severely damaged the control room, incapacitated or killed the control room crew, and caused the submarine to sink. The fire resulting from this explosion in turn triggered the detonation of between five and seven torpedo warheads after the submarine had struck bottom. This second explosion was equivalent to between 2 to 3 tonnes (2.0 to 3.0 long tons; 2.2 to 3.3 short tons) of TNT. It collapsed the first three compartments and all the decks, and destroyed compartments four and five, killing everyone forward of the nuclear reactor compartment. An alternative explanation offered by critics suggested that the crew was not familiar with nor trained on firing HTP torpedoes and had unknowingly followed preparation and firing instructions intended for a very different type of torpedo. Combined with poor oversight and incomplete inspections, the sailors initiated a set of events that led to the explosion.

And the sea will grant each person new hope, as sleep

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