After turning off a computer and desk light and letting them both cool off to an
ID: 908207 • Letter: A
Question
After turning off a computer and desk light and letting them both cool off to an ambient temperature of 25 celsius.A.) What is the total change in entropy for the computer chip for this cooling process? How much total entropy is generated for the chip? ( The chip is made up of 50g silicon, 20g copper, 65g polyvinyl chloride, initially at a temperature of 75 celsius).
B.) Find the specific entropy change for the light bulb in this cooling process. Calculate the specific entropy generated for the bulb. ( the light bulb is initially filled with argon, an ideal gas, at a temperature of 65 celsius and a pressure of 103.8 kPa. Neglet the glass and metal comprising the rest of the bulb.) After turning off a computer and desk light and letting them both cool off to an ambient temperature of 25 celsius.
A.) What is the total change in entropy for the computer chip for this cooling process? How much total entropy is generated for the chip? ( The chip is made up of 50g silicon, 20g copper, 65g polyvinyl chloride, initially at a temperature of 75 celsius).
B.) Find the specific entropy change for the light bulb in this cooling process. Calculate the specific entropy generated for the bulb. ( the light bulb is initially filled with argon, an ideal gas, at a temperature of 65 celsius and a pressure of 103.8 kPa. Neglet the glass and metal comprising the rest of the bulb.) After turning off a computer and desk light and letting them both cool off to an ambient temperature of 25 celsius.
A.) What is the total change in entropy for the computer chip for this cooling process? How much total entropy is generated for the chip? ( The chip is made up of 50g silicon, 20g copper, 65g polyvinyl chloride, initially at a temperature of 75 celsius).
B.) Find the specific entropy change for the light bulb in this cooling process. Calculate the specific entropy generated for the bulb. ( the light bulb is initially filled with argon, an ideal gas, at a temperature of 65 celsius and a pressure of 103.8 kPa. Neglet the glass and metal comprising the rest of the bulb.)
Explanation / Answer
A) Initial temp=T1=75C=75+273=348K
Final temp=T2=25C=25+273=298K
Hot body=silicon chip
m=mass of silicon in chip=50g
C=sp.heat of silicon=0.71 KJ/ kg K
Entropy change=S (Si)=m*c dT=mc ln T2/T1= 50g *(0.71 KJ/ kg K)*ln 298/348=0.05 kg **(0.71 KJ/ kg K)* (-0.15)=-5.32*10^-3 KJ/K
Similarly ,entropy change for copper,
m=mass of copper=20g
C=sp.heat of silicon=384.4 *10^-3 KJ/ kg K
Entropy change=S (cu)=m*c dT=mc ln T2/T1= 20g *(0.384 KJ/ kg K)*ln 298/348=0.02 kg **(0.384 KJ/ kg K)* (-0.15)=-1.15*10^-3 KJ/K
Similarly ,entropy change for PVC,
m=mass of copper=65g
C=sp.heat of silicon=1005J/kg C=
Entropy change=S (PVc)=m*c dT=mc ln T2/T1= 65g *(1005*10^-3 KJ/ kg C)*ln 25/75=0.02 kg **(0.384 KJ/ kg C)* (-1.11)=-0.0277 KJ/C =-0.0277 KJ/283K=-3.45*10^-7kj/k
[1C=273+1=283K]
Total entropy change of chip=S (pvc)+ S (cu)+ S (Si)=( -5.32*10^-3 KJ/K) +( -1.15*10^-3 KJ/K)+( -3.45*10^-7kj/k)=-0.00647 KJ/K
B) entropy change for the light bulb
T1=65C=65+273=338K
T2=25C=25+273=298K
Pressure=p=103.8Kpa
Sp.heat of argon=523 J/kg K
Specific entropy change=C ln T2/T1=523 J/kg K ln 298/338=523 J/kg K (-0.13)=67.99 J/Kg k