(a) (i) Define nuclear fission.
(ii) A certain natural decay series starts with \(^{238}_{92}U\) and ends with \(^{230}_{90}Th\). Each step involves the loss of an alpha or a beta particle. Using the given information, deduce how many alpha beta particpes were emitted.
(b) Consider the equilibrium reaction represented by the following equation:
\(\mathrm{A_2(g) + 3B_2(g) \rightleftharpoons 2AB_3(g)}\); \(\Delta H = +x\mathrm{kJmol}^{-1}\)
Explain briefly the effect of each of the following changes on the equilibrium composition: (i) increase in concentrat of B; (ii) decrease in pressure of the system; (iii) addition of catalyst.
(c) The lattice energies of three sodium halides are as follows:
| Compound |
NaF |
NaBr |
Nal |
| Lattice energy/\(\mathrm{kJmol}^{-1}\) |
890 |
719 |
670 |
Explain briefly the trend.
(d) State the property exhibited by nitrogen (IV) oxide in each of the following reactions:
(i) \(\mathrm{4Cu + 2NO_2 \to 4CuO + N_2}\);
(ii) \(\mathrm{H_2O + 2NO_2 \to HNO_3 + HNO_2}\).
(e) Iron is manufacturcd in a blast furnace using iron ore (\(\mathrm{Fe_2O_3}\)), coke and limestone. Write the equation for the reaction(s) at the: (i) top of the furnace; (ii) middle of the furnace; (iii) bottom of the furnace.
(f) (i) Name two products of destructive distillation of coal. (ii) Give one use of each product in (f)(i).
(a)(i) Nuclear fission
The splitting of a heavy atomic nucleus into two or more lighter nuclei of comparable mass, accompanied by the release of neutrons and a very large amount of energy, usually when the nucleus is struck by a neutron.
(a)(ii) Alpha and beta particles emitted from \(^{238}_{92}\)U to \(^{230}_{90}\)Th
Change in mass number: \(238 - 230 = 8\). Only alpha emission changes the mass number (by 4 each):
\[ \text{number of }\alpha = \frac{8}{4} = 2 \]
Change in atomic number: 2 alphas alone would give \(92 - (2\times 2) = 88\), but the product has Z = 90. Each beta emission raises Z by 1:
\[ 88 + b = 90 \Rightarrow b = 2 \]
So 2 alpha particles and 2 beta particles were emitted.
(b) Equilibrium: A\(_2\)(g) + 3B\(_2\)(g) \(\rightleftharpoons\) 2AB\(_3\)(g); \(\Delta H = +x\) kJ mol\(^{-1}\) (endothermic)
- (i) Increase in concentration of B: equilibrium shifts to the right (forward) to use up the added B, giving more AB\(_3\).
- (ii) Decrease in pressure: the system shifts toward the side with the greater number of gas moles. The left has 4 moles and the right 2 moles, so equilibrium shifts to the left (backward), forming more A\(_2\) and B\(_2\).
- (iii) Addition of a catalyst: no effect on the equilibrium composition; it only speeds up the forward and backward reactions equally, so equilibrium is reached sooner.
(c) Trend in lattice energy of the sodium halides
| Compound | NaF | NaBr | NaI |
|---|
| Lattice energy/kJ mol\(^{-1}\) | 890 | 719 | 670 |
From F\(^-\) to Br\(^-\) to I\(^-\) the ionic radius of the halide increases, so the distance between the Na\(^+\) and the halide ion grows. Lattice energy is inversely related to this interionic distance, so the electrostatic attraction weakens and the lattice energy falls: NaF > NaBr > NaI.
(d) Property of nitrogen(IV) oxide
- (i) 4Cu + 2NO\(_2\) \(\rightarrow\) 4CuO + N\(_2\): nitrogen is reduced from +4 to 0, so NO\(_2\) acts as an oxidising agent.
- (ii) H\(_2\)O + 2NO\(_2\) \(\rightarrow\) HNO\(_3\) + HNO\(_2\): nitrogen goes to +5 (in HNO\(_3\)) and +3 (in HNO\(_2\)), so NO\(_2\) undergoes disproportionation (it is simultaneously oxidised and reduced).
(e) Reactions in the blast furnace
- (i) Top (cooler zone) - reduction of the ore by carbon(II) oxide: \[ \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2 \]
- (ii) Middle - decomposition of limestone and formation of carbon(II) oxide: \[ \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \qquad \text{CO}_2 + \text{C} \rightarrow 2\text{CO} \]
- (iii) Bottom (hottest zone, at the tuyeres) - combustion of coke: \[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \]
(Formation of slag, CaO + SiO\(_2\) \(\rightarrow\) CaSiO\(_3\), also occurs in the lower middle region.)
(f)(i) Two products of the destructive distillation of coal: coke and coal tar (coal gas and ammoniacal liquor are also produced).
(f)(ii) One use of each:
- Coke: used as a fuel and as the reducing agent in the extraction of iron in the blast furnace.
- Coal tar: used as a raw material for making dyes, drugs and antiseptics (and for surfacing roads).
(a)(i) Nuclear fission
The splitting of a heavy atomic nucleus into two or more lighter nuclei of comparable mass, accompanied by the release of neutrons and a very large amount of energy, usually when the nucleus is struck by a neutron.
(a)(ii) Alpha and beta particles emitted from \(^{238}_{92}\)U to \(^{230}_{90}\)Th
Change in mass number: \(238 - 230 = 8\). Only alpha emission changes the mass number (by 4 each):
\[ \text{number of }\alpha = \frac{8}{4} = 2 \]
Change in atomic number: 2 alphas alone would give \(92 - (2\times 2) = 88\), but the product has Z = 90. Each beta emission raises Z by 1:
\[ 88 + b = 90 \Rightarrow b = 2 \]
So 2 alpha particles and 2 beta particles were emitted.
(b) Equilibrium: A\(_2\)(g) + 3B\(_2\)(g) \(\rightleftharpoons\) 2AB\(_3\)(g); \(\Delta H = +x\) kJ mol\(^{-1}\) (endothermic)
- (i) Increase in concentration of B: equilibrium shifts to the right (forward) to use up the added B, giving more AB\(_3\).
- (ii) Decrease in pressure: the system shifts toward the side with the greater number of gas moles. The left has 4 moles and the right 2 moles, so equilibrium shifts to the left (backward), forming more A\(_2\) and B\(_2\).
- (iii) Addition of a catalyst: no effect on the equilibrium composition; it only speeds up the forward and backward reactions equally, so equilibrium is reached sooner.
(c) Trend in lattice energy of the sodium halides
| Compound | NaF | NaBr | NaI |
|---|
| Lattice energy/kJ mol\(^{-1}\) | 890 | 719 | 670 |
From F\(^-\) to Br\(^-\) to I\(^-\) the ionic radius of the halide increases, so the distance between the Na\(^+\) and the halide ion grows. Lattice energy is inversely related to this interionic distance, so the electrostatic attraction weakens and the lattice energy falls: NaF > NaBr > NaI.
(d) Property of nitrogen(IV) oxide
- (i) 4Cu + 2NO\(_2\) \(\rightarrow\) 4CuO + N\(_2\): nitrogen is reduced from +4 to 0, so NO\(_2\) acts as an oxidising agent.
- (ii) H\(_2\)O + 2NO\(_2\) \(\rightarrow\) HNO\(_3\) + HNO\(_2\): nitrogen goes to +5 (in HNO\(_3\)) and +3 (in HNO\(_2\)), so NO\(_2\) undergoes disproportionation (it is simultaneously oxidised and reduced).
(e) Reactions in the blast furnace
- (i) Top (cooler zone) - reduction of the ore by carbon(II) oxide: \[ \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2 \]
- (ii) Middle - decomposition of limestone and formation of carbon(II) oxide: \[ \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \qquad \text{CO}_2 + \text{C} \rightarrow 2\text{CO} \]
- (iii) Bottom (hottest zone, at the tuyeres) - combustion of coke: \[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \]
(Formation of slag, CaO + SiO\(_2\) \(\rightarrow\) CaSiO\(_3\), also occurs in the lower middle region.)
(f)(i) Two products of the destructive distillation of coal: coke and coal tar (coal gas and ammoniacal liquor are also produced).
(f)(ii) One use of each:
- Coke: used as a fuel and as the reducing agent in the extraction of iron in the blast furnace.
- Coal tar: used as a raw material for making dyes, drugs and antiseptics (and for surfacing roads).
