5. The integrated circuits in your cell phone and computer are made from the sem
ID: 693872 • Letter: 5
Question
5. The integrated circuits in your cell phone and computer are made from the semiconductor silicon. The silicon is obtained from a really inexpensive starting material, sand, which is primarily Sio.One step in the purification of silicon is to separate it from solid impurities by forming the gas silicon tetrachloride. Given the following reactions, what is the overall enthalpy change (in kJ) in converting 60 g of silicon dioxide into pure silicon? Reaction DH (kJ) +690 -657 -625 SiO2(s) + 2C(s)-Si(impure s) + 2CO(g) Simpure s) + 2C12(g) SiCl4(g) SiCla(g) 2Mg(s)-2MgC12(s) + Si(s) 8. What is the kinetic energyof a skier weighing 180 lb traveling 65 mph? (2.205 lb = 1 kg, 1 mi = 1.609 km, 1 J-1 kg m2s-2)Explanation / Answer
The reactions are SiO2(s)+2C(s)---->Si( impure S)+ 2CO(g), deltaH= 690 KJ (1)
Si( impure S)+ 2Cl2(g)-------->SiCl4(g), deltaH=-657 KJ (2)
SiCl4(g)+2Mg(s)-------->2MgCl2(s)+ Si(s) ,deltaH= -625 (3)
Eq.1+Eq.2+Eq.3 gives
SIO2(s)+2C(s)+2Cl2(g)+ 2Mg(s)------->2CO+2MgCl2+Si(s), deltaH= 690-657-625=-592 Kj
1 mole of SiO2 produces 592 Kj of heat. Molar mass of SiO2= 60 g/mole
60 g/mole prdouces 592 Kj
2. mass of skier= 160 lb, 2.205 lb= 1 kg, 160 lb= 160/2.205 kg = 72.6 kg, velocity = 65 mph=65*1.609 km/hr=105 km/hr= 105*1000m/(60*60sec)= 29.2 m/sec
Kinetic energy= (1/2)*mV2= 0.5* 72.6* 29.2*29.2 kg m2/sec2 =30951 kgm2/sec2= 30951 Joules
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