QUESTION 8: HEAT
8.1
- Given: Initial volume V0=0.420m3. Initial temperature T0=298 K. Final temperature Tf=358 K.
- Assumption: The volumetric thermal expansion coefficient for aluminium is not provided. We will use a standard value for the linear expansion coefficient of aluminium, αAl=23×10−6K−1. The volumetric expansion coefficient is then γAl=3αAl.
Step 1: Calculate the change in temperature.
ΔT=Tf−T0=358K−298K=60K
Step 2: Calculate the volumetric expansion coefficient for aluminium.
γAl=3×αAl=3×(23×10−6K−1)=69×10−6K−1
Step 3: Calculate the increase in volume.
ΔV=γAlV0ΔT
ΔV=(69×10−6K−1)×(0.420m3)×(60K)
ΔV=0.0017388m3
The increase in volume of the aluminium block is 0.00174m3.
8.2
- Given: Volume V=0.85m3. Temperature T=27∘C. Pressure P=520 kPa. Gas constant R=287J/kg⋅K.
Step 1: Convert temperature to Kelvin and pressure to Pascals.
T=27∘C+273=300K
P=520kPa=520×103Pa
Step 2: Use the ideal gas law PV=mRT to calculate the mass of the gas.
m=RTPV
m=(287J/kg\cdotK)×(300K)(520×103Pa)×(0.85m3)
m=86100442000≈5.1336kg
The mass of the gas is 5.13kg.
8.3
- Given: Initial mass m1=15 kg of CO2. Initial pressure P1=150 kPa. Initial temperature T1=18∘C. Final pressure P2=210 kPa. Final temperature T2=38∘C.
- Assumption: The specific gas constant for CO2 is not given. We will use the universal gas constant Ru=8.314J/mol⋅K and the molar mass of CO2 (MCO2=44.01g/mol=0.04401 kg/mol) to find the specific gas constant RCO2=Ru/MCO2≈188.90J/kg⋅K. However, since the volume of the cylinder is constant and the gas constant for CO2 is the same for both states, it will cancel out in the calculation.
Step 1: Convert temperatures to Kelvin and pressures to Pascals.
T1=18∘C+273=291K
P1=150kPa=150×103Pa
T2=38∘C+273=311K
P2=210kPa=210×103Pa
Step 2: Use the ideal gas law for both states. Since the volume V is constant:
V=P1m1RT1=P2m2RT2
The gas constant R cancels out:
P1m1T1=P2m2T2
Step 3: Solve for the final mass m2.
m2=m1(P1P2)(T2T1)
m2=15kg×(150×103Pa210×103Pa)×(311K291K)
m2=15×1.4×0.935691≈19.6495kg
Step 4: Calculate the mass of carbon dioxide that was added.
Δm=m2−m1=19.6495kg−15kg=4.6495kg
The mass of carbon dioxide that was added is 4.65kg.
8.4
- Given: Initial container capacity Vc0=600ml=600×10−6m3. Initial temperature T0=18∘C. Final temperature Tf=48∘C. Linear expansion coefficient of container αc=10.8×10−6K−1. Volumetric expansion coefficient of toluene γt=1.15×10−3K−1.
Step 1: Calculate the change in temperature.
ΔT=Tf−T0=48∘C−18∘C=30∘C=30K
Step 2: Calculate the volumetric expansion coefficient of the container.
γc=3αc=3×(10.8×10−6K−1)=32.4×10−6K−1
Step 3: Calculate the increase in volume of the toluene.
Since the container is completely filled, the initial volume of toluene Vt0 is equal to the initial volume of the container Vc0.
ΔVt=γtVt0ΔT=(1.15×10−3K−1)×(600×10−6m3)×(30K)
ΔVt=2.07×10−5m3
Step 4: Calculate the increase in volume of the container.
ΔVc=γcVc0ΔT=(32.4×10−6K−1)×(600×10−6m3)×(30K)
ΔVc=5.832×10−7m3
Step 5: Calculate the volume of toluene that will overflow.
ΔVoverflow=ΔVt−ΔVc
ΔVoverflow=2.07×10−5m3−5.832×10−7m3
ΔVoverflow=(20.7×10−6m3)−(0.5832×10−6m3)
ΔVoverflow=20.1168×10−6m3
Step 6: Convert the overflow volume to millilitres.
ΔVoverflow=20.1168×10−6m3×1m31000L×1L1000ml=20.1168ml
The volume of toluene that will overflow is 20.12ml.
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