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Questions for Revision During Covid-19

Atomic Structure

Question 1

Write the electronic configuration for: C, N3-, Fe2+, Cu, Cu+, I and Pb.

Question 2. 

Put the following atoms/ions in order of decreasing size. Explain your answer. The atoms/ions are: Na+, Al3+, Ne, Ar, K+, N3-.

Question 3:

Draw a graph representing all the ionisation energies possible for the Al atom.

Bonding

Question 1

Explain the trends in boiling points for the hydrogen halides.

Question 2

Draw the following molecules/ions: BH2–, NI3, ClF4, SF5–, BO33-, O32+, IO2+, BBr32-

Energetics

Question 1

On strong heating, calcium carbonate decomposes to calcium oxide and carbon dioxide:

CaCO3_{(s)} \rightarrow CaO_{(s)} + CO2_{(g)}

Owing to the conditions under which the reaction occurs, it is not possible to measure the enthalpy change directly.

An indirect method employs the enthalpy changes when calcium carbonate and calcium oxide are neutralized with hydrochloric acid.

i) Write the equation for the reaction of calcium carbonate with hydrochloric acid. State symbols are not required. [ΔH1 is the enthalpy change for this reaction]

ii) The reaction of calcium oxide with hydrochloric acid is

CaO_{(s)} + 2HCl_{(aq)} \rightarrow CaCl2_{(aq)} + H2O_{(l)} \Delta H2

Use the equations in parts (i) and (ii) to complete the Hess’s Law cycle below to show how you could calculate the enthalpy change for the decomposition of CaCO3. Label the arrows in your cycle.

Question 2

Calculate ΔH and ΔS  for the following reaction:

NH_4NO_3_{(s)} + H_2O_{(l)} \rightarrow NH_4^+_{(aq)}+NO_{(3)}- _{(aq)}

Use the results of this calculation to determine the value of ΔGo for this reaction at 25o C, and explain why NH4NO3 spontaneously dissolves in water at room temperature.

Compound              Hfo(kJ mol-1)         S(J mol-1 K-1)

NH4NO3(s)                 -365.56              151.08

NH4+ (aq)                  -132.51               113.4

NO3– (aq)                   -205.0                 146.4

 

Equilibria

Kc

Question 1

Esters are a useful group of compounds due to their distinctive smells. One example
of an ester is ethyl ethanoate, its formation is shown below.

CH_3COOH_{(aq)} + C_2H_5OH_{(aq)} \rightarrow CH_3COO C_2H_5_{(aq)} + H_2O_{(l)}

a) Systems like this are described as being a ‘dynamic equilibrium’. Explain
the term ‘dynamic equilibrium’

b) Write down the expression for the equilibrium constant, Kc, for this reaction.

c) Calculate the value of Kc for this reaction given the equilibrium concentrations below.

[CH3COOH] = 0.08 moldm-3, [C2H5OH] = 0.08 moldm-3, [CH3COO C2H5] = 0.25 moldm-3, [H2O] = 0.1 moldm-3

d) Concentrated sulphuric acid is added to the reaction mixture as it removes water molecules. What effect would this have on the equilibrium position of this system?

Question 2

A mixture of 1.441 g of H2 and 70.24 g of Br2 is heated in a 2.00-L vessel at 700 K. These substances react as follows.

H_2_{(g)}+Br_2_{(g)}\rightarrow 2HBr_{(g)}

At equilibrium, the vessel is found to contain 0.627g of H2. Calculate their equilibrium concentrations and Kc.

Kp

Question 1

Ammonium iodide dissociates reversibly to ammonia and hydrogen iodide.

NH_4I_{(s)}\rightleftharpoons NH_3_{(g)}+HI_{(g)}

At  Calculate the partial pressure of ammonia at equilibrium when a sufficient quantity of ammonium iodide is heated to 

Question 2

For the reaction

AsCl_5_{(g)}\rightleftharpoons AsCl_3_{(g)}+Cl_2{(g)}

at 550 K, the equilibrium constant (Kp) is 9.81kPa. Suppose that 3.150 g AsCl5 is placed in an evacuated 600 ml bulb, which is then heated to 550K.

What is the partial pressure of AsCl5 at equilibrium? (For this question you would need to use Pv=nRT and in the ICE table, the pressure is used instead of moles)