Chemical Engineering 102
Due: Wed. 01/14
Problem Set #1
1.) A tank containing 50 kg of ethanol at 20ºC is fitted with a stirrer that delivers work to the
water at a rate of 0.75 kW. How long does it take for the temperature of the water to rise to 30ºC
if no heat is lost from the water? How long to get to 50ºC? Let Cp = 2.605 kJ/kgºC.
2.) Problem 2.13, except make the following changes: the steel casting weighs 5 kg and is
initially at 600ºC; there is 60 kg of water in a steel tank weighing 10 kg, and 25% of the heat
provided by the steel casting is actually lost to the environment.
3.) Problem 2.23, except the hot water rate is 2.0 kg/s and a third (cold water) stream initially at
5ºC and flowing at 0.75 kg/s is mixed in as well.
4.) Ten kilograms of air (ideal gas) is expanded reversibly at constant pressure from an initial
state of 300 K and 10 bar until the volume triples. Calculate Wt, Qt, ∆Ut, and ∆Ht for the process.
Let Cp = 29 J/molK & MW = 28.851 g/mol.
5.) One mole of an ideal gas, initially at 25ºC and 1 bar is changed to 350ºC and 25 bar by two
different mechanically reversible processes, below. Calculate the total Q, W, ∆U, and ∆H for
each overall process (in kJ). Let Cv = (5/2) R and Cp = (7/2) R.
a.) The gas is first heated isobarically to 350ºC; then compressed isothermally to 25 bar.
b.) The gas is first compressed isothermally to 25 bar, then heating isobarically to 350ºC.
6.) An ideal gas (Cp = 3.5R) undergoes a process from state A to state B. If state A is at 800 K
and 8 bar and state B is at 2 bar, calculate the total Q, W, ∆U, and ∆H if the process is:
a.) one-step adiabatic cooling
b.) two-step, isobaric heating followed by isovolumetric cooling
c.) two-step, isovolumetric cooling, followed by isobaric heating
d.) two-step, isothermal expansion followed by isovolumetric cooling
DRAW EACH PROCESS ON THE SAME PV DIAGRAM (label carefully)
Approximate Answers: (within 25%)
1.) ~30 min to 30ºC; 2.) 30ºC; 3.) 45ºC; 4.) Qt ~ 6000 kJ; 5.) ∆H ~ 10 kJ/mol, a.) Q ~ -7 kJ/mol,
b.) Q ~ 1.6 kJ/mol; 6.) ∆U ~ -5000 J/mol, b.) W ~ -11000 J/mol, d.) W ~ -7000 J/mol