Exam-style questions 1 Renewable and non-renewable energy sources are essential

Question

Exam-style questions 1 Renewable and non-renewable energy sources are essential in modern society a Explain the difference between renewable and non-renewable energy sources b Seate one advantage and one disadvantage of using solar energy to generate electricity. e Hydrogen-axygen fuel cells can be used to provide power for electric vehicles. Hydrogen is stored in 12) 121 anks in the vehicles and a continuous supply of hydrogen must be fed into the cell to produce clectricity In a hydrogen-oxygen fuel cell, the reaction that occurs is equivalent to the combustion of hydrogen: 10.0 mol of hydrogen were fed into a hydrogen fuel cell and 1500kJ of electrical energy was obeained. Calculate the efficiency of the fuel cell. The density of methanol (CH,OH) at 298K is 0.79gcm and the enthalpy change of combustion is -726kjmol.Calculate the energy density of methanol. i [21 üi of hydrogen is more than six times the specific energy of methanol, but some scientists believe that methanol might be a more useful fuel for powering electric vehicles than hydrogen. Explain why this might be the case. 121 It is estimated that there are over 1 billion cars in the world and the majority of these use petrol/gasoline as fuel. a Explain the process by which gasoline is obtained from crude oil. b Octane numbers are often stated on petrol pumps in petrol stations 2 i State what is meant by the octane number of a fuel. äi Explain how cracking can be used to improve the octane number of fuels. [31 Transport contributes a great deal to an individual's carbon footprint. e i Use the data below to calculate the carbon footprint per person for an aeroplane journey from London to New York distance from London to New York fuel consumption of aircraft number of passengers+crew 570km 14.0dm2km- 500 2.00kg carbon dioxide produced per dm of fuel consumed The Ferrari 458 Italia has a fuel consumption of approximately 13.0 dm2 per 100km. Calculate the carbon footprint per person for two people travelling 5570km in a Ferrari 458. Assume that the fuel has the same molecular formula as octane (GHB) and a density of0.700 gcm, ii 15] 3 Uranium-235 is an important fuel for nuclear reactors. In a nuclear reactor the uranium-235 undergoes nuclear fission a Explain what is meant by 'nuclear fission b Explain in terms of nuclear binding energy why uranium-235 undergoes fission rather than fusion c A possible reaction that uranium-235 can undergo is: Calculate the number of neutrons produced in this reaction CHEMISTRY FORTHE IB DIPLOMA O CAMBRIDGED

Explanation / Answer

Q1 a) Renewable resources: Renewable resources are those which can be replenished over short period of time.For example solar energy, wind energy etc

Non renewable resources:A non renewable resources are those which can not be replenished .For example fossil fuels, groundwater etc.

b)

Advantage of solar energy:It is pollution free source and causes no pollution.

Disdvantage of solar energy: The installation cost for solar panels ( as source of solar energy ) is very high.

c) H2 + 1/2O2 --> H2O

delta H = -286 kJ/mol

1 mol of H2 , energy produced = 286 kJ/mol

10 mol , energy produced should be = 286 x 10 = 2860kJ

the energy produced is given as = 1500 kJ

efficeincy = 1500/ 2860 ] x 100 = 52.4 %

Q2 a)

The process by which gasoline is produced is fractional distillation.

Crude oil is separated or partioned in fractions using fractional distillating column.

It is based on the boiling point. The fractions at the top of fractional distillating colum have lower boiling point and the fractions which are at bottom of the column have higher boiling point.The fractions/ components are then processed at the refining unit.

b) 1)Octane number is the measure of ignition quality. It is the number which indicates the antiknocking property of fuel.

ii) Cracking is breaking up large alkanes, So by cracking the large alkanes are made into shorter chain hydrocarbons which have higher octane numer.

Q3

a) Nuclear fission is breaking up of larger nucleus into smaller nuclei.Energy is released in this process.

b) binding energy last neutron in U-236 is 6.4 MeV, the critical energy required for fission is only 5.3 MeV, so when U-235 takes up a neutron, the resulting U-236 nucleus has an excess of 1.1 MeV above the energy which causes fission.

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