General (1st/2nd Law)
What property always increases for isolated systems, according to the Second Law?
Entropy
Which Tds equation would you use for a system undergoing an isochoric process?
Tds = du + Pdv OR Tds = dh - vdP
Tds = du + Pdv
What thermodynamic power cycle is commonly used to model steam power plants?
The Rankine cycle
What term describes the number of moles of a species consumed or produced per mole of reaction?
Stoichiometric coefficient
What property represents the heat released or absorbed when a reaction proceeds under standard conditions?
Standard heat of reaction
The maximum possible efficiency of a heat engine depends only on the temperatures of what two things?
The hot and cold thermal reservoirs
What is the ratio of actual work output to ideal work output of a turbine called?
Isentropic efficiency of a turbine
Adding a reheater between turbine stages in a steam power plant increases efficiency by raising the average value of what property during the expansion process?
Temperature
Changes in species molar flow (i.e., nout - nin) equal their stoichiometric coefficient times what quantity?
The extent of reaction
In an energy balance on a reacting system, what term accounts for chemical energy differences between reactants and products?
The heat of reaction term
What are the two types of policy and engineering options we have when it comes to addressing climate change? (re: energy & environment)
Mitigate or Adapt
How is an isentropic process defined in terms of entropy and typical physical characteristics?
Δs = 0
reversible, adiabatic process
For an ideal refrigeration system, define the coefficient of performance (COP) for a refrigerator and relate it to the COP of a heat pump.
COPR = QL / Win
COPHP = COPR + 1
When a reactant is fed in greater amount than required by stoichiometry, it is said to be in what condition?
In excess
What is the standard heat of formation of a compound, and how is it defined?
Enthalpy change when a mole of the compound is formed from its constituent elements in their standard states at a specified standard condition (usually 25°C and 1 atm).
What carnot refrigeration device will have a higher COP? A refrigerator or an AC?
AC (bc the Delta T is smaller between AC and environment)
On a Ts diagram, where is the isentropic exit state in reference to the actual exit state?
Actual is on the right hand side of the isentropic
Consider a simple ideal Rankine cycle with fixed turbine inlet conditions. What is the effect of lowering the condenser pressure on turbine work out?
Work output increases
In material balances with chemical reactions, when might an atomic balances be preferred over molecular species balances, and what is conserved in such balances?
Atomic balances are preferred because they are independent of the reaction path and remain valid even when multiple reactions occur. In atomic balances, the total number of atoms of each element (C, H, O, N, etc.) is conserved.
How is the standard heat of reaction related to the standard heats of formation of reactants and products, and conceptually how do these two quantities differ?
Heat of reaction = Sum (v Heat of formation)prod - (v Heat of formation)react
A heat engine receives 800 kJ of heat from a 600 K thermal reservoir and rejects heat to a 300 K reservoir. If it operates at the maximum possible (Carnot) efficiency, how much work does it produce?
ηCar = 1 - (TL / TH)
= 1 - (300/600) = 0.5
ηCar = W / QH
W = ηCar (QH) = 0.5(800 kJ)
= 400 kJ
Air is compressed isentropically from 100 kPa and 300 K to 900 kPa. Assuming air behaves as an ideal gas with k=1.4, what is the outlet temperature?
T2/T1 = (P2/P1) ^ ((k-1)/k)
T2/T1 = (900/100) ^ (0.4/1.4)
T2/T1 = 1.87
T2 = 561 K
Steam enters a turbine at 3 MPa and 450°C with h1=3271 kJ/kg. It expands isentropically to 10 kPa, where the exit enthalpy is h2=2220 kJ/kg. What is the turbine work per kg of steam?
wt = h1 - h2 = 3721 - 2220
= 1051 kJ/kg.
For the rxn: A + 2B → C a reactor is fed 100 mol of A and 300 mol of B. If there is 60% conversion of A, what is the molar flow rate of C leaving the reactor?
60 mol of C
Using the standard heats of formation:
Del H_f (CH4) = -75
Del H_f (CO2) = -394
Del H_f (H2O) = -286
Del H_f (O2) = 0
Calculate the standard heat of reaction for
CH4 + 2O2 → CO2 + H2O
Del H_r = (v Delt Hf)prof - (v Delt Hf)react
-891 kJ/mol