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Sch 2106 : Physical Chemistry Question Paper
Sch 2106 : Physical Chemistry
Course:Bachelor Of Science In Environmental Horticulture
Institution: Jomo Kenyatta University Of Agriculture And Technology question papers
Exam Year:2012
JOMO KENYATTA UNIVERSITY
OF
AGRICULTURE AND TECHNOLOGY
University Examinations 2012/2013
FIRST YEAR FIRST SEMESTER EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE IN ENVIRONMENTAL HORTICULTURE/LAND RESOURCE PLANNING AND MANAGEMENT/ANIMAL HEALTH
SCH 2106 : PHYSICAL CHEMISTRY
DATE: AUGUST 2012 TIME: 2 HOURS
INSTRUCTIONS: ANSWER QUESTION ONE (COMPULSORY) AND
ANY OTHER TWO QUESTIONS.
______________________________________________________________________
USEFUL INFORMATION:
00C = 273.15K
R = 8.314Jmole-1K-1
= 0.08206 litre-atm mole1K-1
1 atm pressure = 760mmHg
= 101325 Nm-2
S.T.P (gases) = 1atm pressure, 00C
R.A.M. (C = 12.011, N = 1.008)
R.F.M. (CCl4 = 153.8, SiCl4 = 169.9)
QUESTION ONE (30 MARKS)
(a) Explain the concept of an ideal gas. [3 marks]
(b) A sample of an ideal gas at S.T.P. occupies a volume of 4 litres. Determine the number of mole of the gas. [3 marks]
(c) Determine the pH of a solution with [OH-] = 0.15 M. [3 marks]
(d) Express Raoult’s law in words. [3 marks]
(e) The solubility product of Ba(OH)2 at 250C is 5.0 x 10-3 mol3litres-3. Compute the number of mole of Ba2+ ions in 500cm3 of a saturated Ba(OH)2 solution at 250C. [4 marks]
(f) When 4.1g of gaseous methane, CH4, is completely burnt in oxygen at 250C to form carbon dioxide and liquid water, 227.32kJ of energy is liberated:
(i) Express this information in the form of a thermochemical
equation. [2 marks]
(ii) Express the energy change in kJ mole-1. [3 marks]
(g) State three factors that influence the rate of a chemical reaction.
[3 marks]
(h) State the law of mass action. [3 marks]
(i) An aqueous solution of ammonium chloride turns litmus purple. Explain, using relevant equations. [3 marks]
QUESTION TWO (20 MARKS)
(a) At 1400K Kp for the reaction
H2O(g) + CH4(g) ? CO(g) + 3H2(g),
is 6.2 x 104. Determine the value of Kc at this temperature.
[3 marks]
(b) Given:
H2(g) + I2(g) ? 2HI(g) ,
Kc = 57.0 at 700K. If 0.1 mole of H2(g) is allowed to react with 0.1 mole of I2(g) in a 1 litre vessel at 700K, what are the equilibrium concentrations of H2(g), I2(g) and HI(g)? [8 marks]
(c) 0.23 mole of helium gas and 0.27 mole of nitrogen gas are contained in a 15 litre vessel at 250C. Determine the pressure, in atmospheres, of the gas mixture. [5 marks]
(d) 0.714g of an ideal gas occupies 1.0 litre at STP. Determine the molar mass of the gas. [4 marks]
QUESTION THREE (20 MARKS)
(a) For the chemical cell:
Mn|Mn2+(0.5M)||Pb2+(1.5M)|Pb,
and given that the standard reduction potentials for the half-cells Mn|Mn2+ and Pb|Pb2+ are -1.180V and -0.126V respectively:
(i) From the half-cell reactions deduce the overall cell reaction.
[3 marks]
(ii) Determine the emf of the cell at 250C. [4 marks]
(b) The vapour pressures of pure CCl4 and pure SiCl4 at 250C are 114.9 mmHg and 238mmHg respectively. Assuming ideal behavior, determine the vapour pressure of a solution containing 50g of each of the two liquids. [6 marks]
(c) (i) State Hess’s Law. [3 marks]
(ii) The molar enthalpines of combustion at 250C, of ethene (C2H4); hydrogen H2(g); and ethane C2H6 are -1411.59kJ,
-285.56kJ and -1558.30kJ respectively.
Determine the enthalpy change of the reaction
C2H4(g) + H2(g) = C2H6(g) [4 marks]
QUESTION FOUR (20 MARKS)
(a) Explain the following terms as used in chemical kinetics:
(i) Order of reaction. [2 marks]
(ii) Half-life. [2 marks]
(b) Explain the term osmosis. [2 marks]
(c) Explain the effect of temperature on the rate of a chemical reaction. [3 marks]
(d) State the Chatelier’s principle. [3 marks]
(e) Using an example, explain the term buffer action. [5 marks]
(f) A weak acid HA has Ka = 1.8 x 10-4. Determine the pH of an aqueous solution made by dissolving 0.17 mole of the acid to make 1 litre of solution. [3 marks]
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