Chemistry_2013_STPM term 2_Objectives

The standard enthalpy of formation of CH₃ N H N H₂ , CO₂ and H₂O are

+53 kJ mol^-1 , −393 kJ mol^-1 and −286 kJ mol^-1 respectively. The standard enthalpy change for the following reaction is −5116 kJ.

4 CH₃ N H N H₂ , CO₂ (I) + 5N₂O₄ (I) → 4CO₂ (g) + 12H₂O (I) + 9N₂ (g)

What is the standard enthalpy of formation of N₂O₄?

• − 20 kJ mol^-1

• + 20 kJ mol^-1

• − 100 kJ mol^-1

• + 100 kJ mol^-1

The standard enthalpies of formation of CaCO₃ and BaCO₃ are − 1206.9 kJ mol^-1 and − 1218.8 kJ mol^-1 respectively. Which statement explains the differences in these values?

• The ionisation energy of Ca is higher than that of Ba.

• The enthalpy of atomisation of Ca is lower than that of Ba.

• The lattice energy of BaCO₃ is higher than that of CaCO₃.

• Al is the strongest reducing agent.

• Al³⁺ ion can be reduced by Br^- ion.

• Cu can be oxidised by Br₂ or Ag⁺ ion.

• Br₂ is a strongest oxidising agent than Cu²⁺ ion.

What can be deduced from the above data?

• Mn²⁺ ion is a strongest reducing agent than Br^- ion.

• Cu is deposited when aqueous solutions of Mn²⁺ and Cu²⁺ ions are added together.

• The cell diagram for the oxidation of Cu by Br₂ is Cu(s) l Cu²⁺ ∥ Br₂ (aq) , Br^- (aq)∣ Pt(s)

• The reaction between MnO₂ and Br^- ion does not occur spontaneously under standard conditions.

Is a reducing agent Z as added to beaker II, the graph representing the change in the e .m .f . of the above cell is

• 
• 
• 
• 

The purpose of the process is to

• purify aluminium

• increase of the mass of aluminium

• polish the surface of aluminium

• form a thicker oxide layer on aluminium

The first ionisation energy generally increases across a period in the Period Table. Which statement explains why the first ionisation energy of sulpur is lower than that of phosphorus?

• The electrons in the p orbitals of sulphur experiences greater electrostatic repulsion that of phosphorus.

• The sulphur atom has more electrons than phosphorus atom.

• The S -S bond is weaker than the

  P -P bond.

The arrangement of the elements according to the ascending order of their proton number is

• X , Y , Z

• X , Z , Y

• Z , X , Y

• Z , Y , X

Which oxide of an element dissolves in water to form an acidic solution?

• Sodium

• Magnesium

• Silicon

• Phophorus