Chemical Equations and Reactions Questions

Answer ALL the questions given. [50 marks]

 

Question 1

 

This question is about the equilibrium of chemical reaction.

 

 

 

The chemical equation below represents the reaction between 2.67g of CH3COOH and 3.40g NH3 in a total volume of 1L solution.

 

 

CH3COOH (aq) + NH3 (aq) ↔ CH3COONH4 (aq)

 

 

 

(a)

Calculate the number of moles and the concentration of each reactant in this reaction.

[4]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(b)

Determine the limiting reagent in this reaction.

[1]

 

 

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(c)

If the concentration of CH3COOH, NH3 and ammonium acetate, respectively, is 0.0021M, 0.0167M and 1.9 x 10-4 M at equilibrium, determine the Kc of the reaction in three decimal places.

[2]

 

 

 

 

 

 

 

 

 

 

 

 

 

Total for Question 1 =

[7]

 

 

 

 

 

 

Question 2

This question is about chemical reaction equilibrium.

The equilibrium constant Kc for the reactions A2 (g) + B2(g) ⇆ 2 AB (g) is 43.0 at 500K. Given the initial concentrations are [A2] = 0.003M and [B2] = 0.005M.

 

  1. Write the expression for the equilibrium constant (Kc) for this reaction. [2]

 

 

 

 

 

 

 

 

 

 

  1. Determine change in molarity for each of the reactants and products. [4]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. Calculate the equilibrium concentrations of A2, B2, and AB at 500K if the initial [2] concentrations are [A2] = 0.003M and [B2] = 0.005M.

 

 

 

 

 

 

 

 

 

 

 

 

Total for Question 2 = [8]

Question 3

 

This question is about acid-base equilibrium.

 

 

 

The acid HA reacts with the base XH3 in an aqueous solution, to form XH4+ and A.

 

(a)

Write the balanced chemical equation for this reaction.

[1]

 

 

 

 

 

 

 

 

 

 

(b)

Identify the conjugate acid-base pairs in the reaction above.

[1]

 

 

 

 

 

 

 

 

 

 

 

 

(c)

Explain the basic properties of XH3 in terms of Bronsted-Lowry theory and Lewis theory. [4]

 

 

 

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Total for Question 3 = [6]

 

 

 

 

Question 4

This question is about acid-base equilibrium.

Pyridine is a compound that can act as weak base with the Kb of 1.5 x 10-9. It dissociates in water following the chemical reaction:

 

C5H5N (aq) + H2O (l) ⇆ HC5H5N+ (aq) + OH (aq)

 

The Kw of water is given as 1.0 x 10-14.

 

  1. Write the balanced chemical equations for principal and subsidiary reactions (include [2] state symbols and constant values).

 

 

 

 

 

 

 

 

  1. (i) Calculate the concentration of hydroxide ion, [OH] and pyridinium [HC5H5N+] [5] at equilibrium in a 0.0045M solution of pyridine.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(ii) Determine the pH of the solution. [3] Total for Question 4 = [10]

Question 5

This question is about electrochemical cells.

 

The following diagram shows the electrochemical cell with a redox reaction between 1.0M copper (II) nitrate and 1.0M silver nitrate at standard state conditions. The reaction produces hairlike crystals of silver metals.

word image 2848

  1. Label the following option in the diagram correctly and identify the direction of electron [2] flow.

[Anode, cathode, flow of electrons, wire]

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  1. Write the half equations and the balanced redox equation for the reaction above. [3]

 

Anode : ………………………………………………………………………………… Cathode : …………………………………….………………….…………………….

Redox : ………………………………….……………………….……………………

  1. Identify the species acting as the following component in this electrochemical cell. [2]

Oxidizing agent : ……………..………….…………………………………………….

Reducing agent : ……………………………………………………………………….

  1. Explain why the copper metal displaces the silver ion in the experiment above. [1]

Justification: ……………………………………………………………………………..

 

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Total for Question 5 = [8] Question 6

This question is about thermochemistry.

 

  1. Describe a chemical reaction that can function as an open system by identifying the [3] matter and energy involved.

 

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  1. Do you think an isolated system is present in our daily life? Why? [2]

 

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  1. Calculate the standard enthalpy of formation of carbon disulfide (CS2) from its elements [4]

[C (s) + 2S (s) → CS2 (l)], given that

 

C (graphite) + O2 (g) → CO2 (g) ∆𝐻𝑟𝑥𝑛° = −393.5 𝑘𝐽/𝑚𝑜𝑙

S (rhombic) + O2 (g) → SO2 (g) ∆𝐻𝑟𝑥𝑛° = −296.4 𝑘𝐽/𝑚𝑜𝑙

CS2 (l) + 3O2 (g) → CO2 (g) + 2SO2 (g) ∆𝐻𝑟𝑥𝑛° = −1073.6 𝑘𝐽/𝑚𝑜𝑙

 

 

 

 

 

 

 

 

 

 

  1. Determine whether formation of carbon disulfide is an exothermic or endothermic [2] reaction. Why?

 

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Total for Question 6 = [11]

 

 

 

[Total marks = 50] ~ END OF ASSESSMENT ~

 

 

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