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9701/23

Chemistry 9701/23 — May/June 2010

Cambridge AS Level · AS Level Structured Questions · worked solutions for every part, with the mark scheme

5
questions
60
marks
75
minutes

Topics Nitrogen and Sulfur · Chemical Bonding · Electrochemistry · Atomic Structure · Introduction to Organic Chemistry · Carbonyl Compounds · +11 more

Q1Chemical EnergeticsReaction KineticsNitrogen and SulfurChemical BondingElectrochemistryFree sample

Hydrazine, N2H4\text{N}_2\text{H}_4, can be used as a rocket fuel and is stored as a liquid. It reacts exothermically with oxygen to give only gaseous products.

The enthalpy change of a reaction such as that between hydrazine and oxygen may be calculated by using standard enthalpy changes of formation.

(a)

Define the term standard enthalpy change of formation, ΔHf⊖\Delta H_f^\ominus.

3M
(b)

Hydrazine reacts with oxygen according to the following equation.

N2H4(l)+O2(g)→N2(g)+2H2O(g)\text{N}_2\text{H}_4(\text{l}) + \text{O}_2(\text{g}) \rightarrow \text{N}_2(\text{g}) + 2\text{H}_2\text{O}(\text{g})
4M
(i)

Use the data in the table to calculate the standard enthalpy change of this reaction.

compoundΔHf⊖/kJ mol−1\Delta H_f^\ominus / \text{kJ mol}^{-1}
N2H4(l)\text{N}_2\text{H}_4(\text{l})50.6
H2O(g)\text{H}_2\text{O}(\text{g})-241.8
ΔH⊖=........................................ kJ mol−1\Delta H^\ominus = \text{........................................ kJ mol}^{-1}
(ii)

Although the above reaction is highly exothermic, hydrazine does not burn spontaneously in oxygen.

Suggest a reason for this.

(iii)

Suggest why using hydrazine as a rocket fuel could be regarded as being 'environmentally friendly'.

(c)

The bonding in hydrazine is similar to that in ammonia.

4M
(i)

Showing outer-shell electrons only, draw a 'dot-and-cross' diagram of an ammonia molecule.

(ii)

Draw a diagram to show the three-dimensional shape of an ammonia molecule.

(iii)

Draw a diagram to show the shape of a hydrazine molecule.

Show clearly which atom is joined to which and show clearly the value of one bond angle.

(d)

Deduce the oxidation state of nitrogen in hydrazine.

1M

The rest of this paper

4 more questions
  • Q2Atomic Structure · Atoms, Molecules and Stoichiometry · Electrochemistry12M
  • Q3Group 2 · Nitrogen and Sulfur · Group IV (Group 14) · Atomic Structure · States of Matter · Chemical Bonding · Chemical Periodicity12M
  • Q4Introduction to Organic Chemistry · Carbonyl Compounds · Halogen Compounds · Hydrocarbons9M
  • Q5Introduction to Organic Chemistry · Organic Synthesis · Carbonyl Compounds · Hydroxy Compounds15M
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