Question

3. (a)(i) Define nuclear fission. (ii) A certain natural decay series starts with ₂₉³⁸U and ends with ₉₀²³⁰Th. Each step involves the loss of an alpha or a beta particle. Using the given information, deduce how many alpha and beta particles were emitted.
(b) Consider the equilibrium reaction represented by the following equation: A2(g)+3B2(g)⇌2AB3(g); ΔH=+xkJmol⁻¹. Explain briefly the effect of each of the following changes on the equilibrium composition: (i) Increase in concentration 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 | NaI
Lattice energy /kJmol⁻¹ | 890 | 719 | 670
Explain the trend.
(d) State the property exhibited by nitrogen (IV) oxide in each of the following reactions:
(i) 4Cu+2NO2→4CuO+N2;
(ii) H2O+2NO2→HNO3+HNO2;
(e) Iron is manufactured in a blast furnace using iron ore (Fe2O3), coke and limestone. Write the equation for the reaction(s) at the top of the furnace; (ii) middle of the furnace; (iii) bottom of the furnace; (i) Name two products of destructive distillation of coal; (ii) Give one use of each product in 3(f)(i).

Accepted Answer

(a)(i) Nuclear fission is a process by which a heavy nucleus splits into lighter nuclei of comparable masses, with the release of energy. (ii) Let a represent the number of beta particles and b represent the number of alpha particles. Since beta particle does not have mass, the difference between the mass of ₂₉³⁸U and ₉₀²³⁰Th will be the mass of alpha particles: mass of alpha particle = 238−230 = 8. Since one alpha particle has a mass of 4, there are two alpha particles. b=2. Substituting b=2 into the nuclear equation and balancing: ₂₉³⁸U → ₉₀²³⁰Th + a(−1⁰β) + 2(₂⁴α). 92=90+a(−1)+2(2); 92=90−a+4; a=94−92=2. So two beta particles are also involved. (b)(i) The equilibrium position shifts to the right, favouring production of more AB3. (ii) The equilibrium position shifts to the left, favouring production of more A2 and B2 (since there are more moles of gas on the reactant side). (iii) No change; a catalyst alters both the forward and backward reaction rate alike, so equilibrium position is unaffected. (c) Of the three halogens, fluorine is the most electronegative. This is why NaF has the highest lattice energy. Generally speaking, for a given cation, the lattice energy increases as the electronegativity increases and vice versa. (FNaBr>NaI decreasing lattice energy.) (d)(i) Oxidizing property (NO2 oxidizes Cu to CuO while itself being reduced to N2). (ii) Acid anhydride (NO2 disproportionates in water to form nitric and nitrous acids). (e)(i) Top of the furnace: Fe2O3+3CO→2Fe+3CO2. (ii) Middle of the furnace: CaCO3 →(Δ) CaO+CO2. (iii) Bottom of the furnace: C+O2→CO2; then CO2+C→2CO. (f)(i) The products of destructive distillation of coal are coke, coal tar, coal gas and ammoniacal liquor. (ii) Coke is used in the extraction of metals; coal tar is used for the synthesis of many chemical substances; coal gas is utilized as fuel; ammoniacal liquor is used for making fertilizers.

WAEC Chemistry 2012 Theory — Question 3

Sign up free to unlock