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Sch2106:Physical Chemistry Question Paper
Sch2106:Physical Chemistry
Course:Bachelor Of Science In Public Health
Institution: Meru University Of Science And Technology question papers
Exam Year:2011
QUESTION ONE (30 MARKS)
a) Define the following terms (6 Marks) i. Universe; in terms of its composition. ii. System iii. Surroundings b) Explain the relationship between the terms in (a) above. (2 Marks) c) Give the sign of entropy change when: i. Steam condenses into water. ii. A solute crystallizes from a solution iii. Dissolving sodium chloride crystals in a bowl of water. iv. Evaporating a beaker of liquid bromine at room temperature. d) A sample of a gas expands in volume from 2.0litre to 6.0 litres at constant temperature. Calculate the work done in joules by the gas if it expands against a constant external pressure of 1.2 atmosphere ????: 1 ????????????h?????? = 105???? = 105????-2: 102???? = 100?? ;???? = 10-3??3 . (4 Marks) e) Write expression for the equilibrium constant, kc for the following reactions i. ???? ???? + ??2?? ?? ? ??3??+ ???? + ??-(????) (2 Marks) ii. 2??????) + ??2(??) ? 2????2(??) (2 Marks) f) i) What is a Lewis acid? (2 Marks) ii) Identify the Lewis acid and Lewis base in each of the following reactions; ??2??5????2??5 + ????????3 ? ??2??5 2??????????3 and ????2+ ???? + 4????-(????) ? ???? ???? 4 1(????) . (2 Marks) g) Explain the difference between electrolytic cell and voltaic (galvanic) cell. (4 Marks)
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QUESTION TWO (20 MARKS)
a) i) Define the rate of a chemical reaction (2 Marks) ii) In a certain experiment, the rate of conversion of cyclopropane into propene was studied. The decrease in the concentration of cyclopropane with time was recorded while the increase in the concentration of propene with time was also recorded. Assuming that at the beginning of the experiment the concentration of propane was zero, draw a well labeled sketch graph to show change in the concentration of reactant and product with time for the reaction;
Cyclopropane propene (4 Marks)
iii) Write the rate law for the reaction cyclopropane propene (2 Marks)
iv) If the conversion of cyclopropane into propene would be represented as A B What is the order of the reaction for this reaction? Given A= cyclopropane and B= propene. (2 Marks) b) i) State the law of mass action. (2 Marks) ii) Consider the reaction between nitrogen and hydrogen, 3??2 ?? + ??2(??) ? 2????3(??) Write the expression for mass action. (2 Marks) c) Determine the values of kp for the reactions shown below (6 Marks) i. 2????2 ?? + ??2 ?? ? 2????2 ?? ; ???? = 2.8 × 102???? 1000?? ii. ??2 ?? + ??2 ?? ? 2???? ?? ; ???? = 5.02 × 101???? 445°?? ?? = 0.0821?? ?????? ??????-1??-1
QUESTION THREE (20 MARKS)
a) i) What is a triprotic acid? (2 Marks) ii) Give an example of a triprotic acid and using the relevant chemical equations indicate how the named acid ionizes in aqueous solution. (4 Marks) iii) Ammonia and hydrofluoric acid react in aqueous solution to form conjugate acid-base pairs. Write a balanced chemical equation for this reaction and identify the conjugate acid- base pairs in the aqueous solution. (2 Marks) b) Hot springs are common in the Great Rift Valley in Kenya and the country has utilized the resource for the generation of electricity. A sample of water from one of the hot springs wells at 40°?? has an ??+ of 2.34 × 10-6??. What is the ????+ in the sample? ???? = 2.92 × 10-14???? 313?? . (4 Marks) c) i) Explain the meaning of the term “electrolysis”. (2 Marks) ii) What is the function of an electrolytic cell? (2 Marks) iii) A current of 1.26A is passed through an electrolytic cell containing dilute sulphuric acid solution for 7.44 hours. The overall reaction is 2??2?? ?? ? 2??2 ?? + ??2(??).
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Calculate the volume of each of the gaseous products assuming that the measurements were carried out at STP. (4 Marks)
???????? ?? = 0.08314?? ?????? ??????-1??-1?????? ?? = 298??,?? = 1 ??????
NB:
At the anode: 2??2?? ?? ? ??2 ?? + 4??+ ???? + 4??-.
At the cathode 2 2??+ ???? + 2??- ? ??2(??)
QUESTION FOUR (20 MARKS)
a) i) Define a binary solution. (1 Mark) ii) Give the mathematical expression for the total vapour pressure of a binary solution and explain the symbols used. (3 Marks) iii) A solution is made by dissolving 218g of glucose in 460ml of water at 30°??. Calculate the mole fraction for both glucose and water in the solution, and hence the vapour pressure of glucose. (7 Marks) (Molar mass of glucose = 180.2gmol-1; molar mass of water = 18.02gmol-1, vapour pressure of pure water at 30°?? = 31.83mmHg)
b) i) What is the solubility product of a compound? (2 Marks) ii) Silver bromide AgBr(s) dissociates in water as shown by the equation ???????? ?? ? ????+ ???? + ????- ???? ,?????? = 7.7 × 10-13
Calculate the molar solubility of AgBr(s) at equilibrium. (6 Marks)
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