A Level Chemistry - Questionbank

Homogeneous and heterogeneous catalysts

Question 1

The Haber process is used in industry to convert nitrogen and hydrogen to ammonia. The formation of ammonia gas is exothermic. 

a. Sketch the enthalpy profile for the Haber process in the absence of a catalyst.

b. On the same diagram, sketch the enthalpy profile for the Haber process in the presence of a catalyst.

c. Label the activation energy on one of the profiles.

Hard

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Question 2

The activation energy for the uncatalysed decomposition of ammonia to its elements is +335 kJ mol−1.

a. Write the equation for this reaction, including state symbols.

b. The enthalpy of reaction for this decomposition is +92 kJ mol−1. Calculate the activation energy for the uncatalysed formation of ammonia from nitrogen and hydrogen.

c. If tungsten is used as a catalyst, the activation energy changes. Explain how it will change.

Hard

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Question 3

a. Ammonia is a very important industrial chemical with many uses including the manufacture of other chemicals. 

The first step in the production of nitric acid involves the reversible reaction of gaseous ammonia in air to form nitrogen(II) oxide gas and water vapour. 

Construct an equation for this reaction. Include state symbols.

b. For this reaction, a fine mesh is powder-coated with a mixture of platinum and rhodium catalysts. 

Deduce the type of catalysis involved in the formation of nitrogen(II) oxide. Explain your answer.

Medium

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Question 4

a. The decomposition of 3% hydrogen peroxide solution into water and oxygen is a very slow chemical reaction. Construct an equation for this reaction. Include state symbols.

b. The decomposition of 3% hydrogen peroxide solution can be catalysed by different chemicals including solid manganese dioxide and catalase solution. Deduce the type of catalysis involved in the reaction using each catalyst. Explain your answer.

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Question 5

For the exothermic decomposition of hydrogen peroxide, manganese dioxide gives a greater increase in the rate of reaction than catalase solution. 

a. Sketch a reaction pathway diagram for the reaction using each catalyst. 

b. Label the diagram to show the enthalpy change, ΔH, and the activation energy, E , for each reaction.

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Question 6

a. Gaseous A and B were added together to produce C as shown.

A (g) + 2B (g) C (g)

The figure shows the production of C over time.

i. Sketch a line to show what happens to the concentrations of A and B during the progress of the reaction.

ii. Label the point at which an equilibrium is first established.

b. Explain how the addition of a catalyst affects the rate and yield of the reaction in (a)

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Question 7

Which statements correctly describe how a catalyst works?

A. A catalyst has no effect on the enthalpy change of the reaction

B. A catalyst increases the rate of the forward reaction only

C. A catalyst increases the average kinetic energy of the reacting particles

D. The mass of the reactant changes after the reaction

Easy

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Question 8

The addition of a catalyst to a reaction provides an alternate mechanism with

A. Lower activation energy and lower reaction rate

B. Lower activation energy and higher reaction rate

C. Higher activation energy and lower reaction rate

D. Higher activation energy and higher reaction rate

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Question 9

Which of the following is involved in the Haber process?

A. a heterogeneous iron catalyst

B. a homogeneous iron catalyst

C. a heterogeneous vanadium catalyst

D. a homogeneous vanadium catalyst

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Question 10

The oxidation of butadiene, CH2=CHCH=CH2 , using air or oxygen, produces the molecule crotonaldehyde, CH3CH=CHCHO. 

One method of oxidation is to pass a mixture of butadiene and oxygen through a hot aqueous solution of palladium(II) ions, Pd2+ (aq), which catalyse the reaction. 

Which statement about the action of the Pd2+ (aq) ions is not correct?

A. Pd2+ (aq) lowers the activation energy for the reaction.

B. Pd2+ (aq) increases the energy of the reacting molecules.

C. When Pd2+ (aq) is used, the reaction proceeds by a different route.

D. Changing the concentration of the Pd2+ (aq) affects the rate of oxidation.

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