Chemistry STPM : Semester 2

Consider the following bond enthalpies.

Bond ------ Enthalpy (kJ mol^-1)

Br – Br ---------- 194

H – Br ---------- 362

C – H ----------- 414

C - Br ----------- 285

What is the enthalpy change for the reaction in diagram?

• -1255 kJmol^-1

• -39 kJmol^-1

• +39 kJmol^-1

• +1255 kJmol^-1

The following data are needed for this question.

∆H_f^Ɵ (CO(g)) = –111 kJ mol^-1

∆H_f^Ɵ (CO­₂(g)) = –394 kJ mol^-1

∆H_f^Ɵ (Fe₂O₃(s)) = –822 kJ mol^-1

Carbon monoxide reacts with iron(III) oxide.

3CO(g) + Fe₂O₃(s) → 3CO₂(g) + 2Fe(s)

What is the enthalpy change when 55.8 g of iron are produced by this reaction?

• –27.0 kJ

• –13.5 kJ

• +13.5 kJ

• +27.0 kJ

Copper reacts with dilute nitric acid to produce nitrogen dioxide gas. The balanced ionic equation is given.

Cu + 2H⁺ + 2HNO₃ --> Cu²⁺ + 2NO₂ + 2H₂O

Which of the following is correct?

• A

• B

• C

• D

Which of the following will occur in the cell shown ?

• The blue colour in Y will become less intense.

• The mass of the electrode in Y will decrease.

• The concentration of the solution in X will increase.

• Electrons will flow from X to Y through the salt bridge.

The table shows the successive ionisation energies for an element X.

What could be the formula of the fluoride of X ?

• XF

• XF₂

• XF₃

• XF₄

X, Y and Z are elements in Period 3 of the Periodic Table.

A mixture containing the oxides of X, Y and Z was dissolved in excess dilute sulfuric acid and filtered. The oxide of Z was collected as a residue. When excess dilute sodium hydroxide was added to the filtrate, only a white precipitate of the hydroxide of Y was formed.

What are the possible identities of X, Y and Z?

• A

• B

• C

• D

Samples of magnesium carbonate, MgCO₃, are placed in crucibles R and S.

The sample in crucible R is heated until there is no further loss in mass, and then allowed to cool.

The sample in crucible S is left unheated.

Dilute hydrochloric acid is then added to both crucibles.

On adding the dilute hydrochloric acid, which observations are correct?

• A

• B

• C

• D

In the reaction shown, M represents a Group 2 element.

MO₂ → MO + ½ O₂

Which statement about this reaction is correct?

• It is a redox reaction.

• The anion in MO₂ contains 8 electrons.

• The lattice energy of MO₂ is greater in magnitude than the lattice energy of MO.

• 

In the preparation of silicon, silicon dioxide is heated with magnesium.

SiO₂ + 2Mg --> 2MgO + Si

The product mixture contains MgO and Si only. To separate the silicon from the product mixture, students proposed the following two possible methods :

1. Shake the mixture with aqueous hydrochloric acid and filter.

2. Heat the mixture gently and collect the evaporated silicon.

Which methods would work?

• 1 and 2

• 1 only

• 2 only

• neither 1 or 2

Germanium is between silicon and tin in Group 14. Which one of the following statements about germanium chemistry is least likely to be true?

• The element has a diamond type structure

• The oxide will dissolve in aqueous sodium hydroxide

• The element is a better electrical conductor than tin

• Germanium-oxygen covalent bonds will be weaker than silicon-oxygen bonds.