Review for Midterm # 1
Michael Roders
Samantha Sweeney
True/False
For any substances, Cp,m is always greater than Cv,m.
False
Cp = Cv + R holds for ideal gases only
Please define the two major differences between
ideal gases and real gases.
1.
2.
No molecular volume
No interactions (except collisions) between any two molecules
Experimentally, under what conditions can a real gas
be approximated as an ideal gas?
Low pressure
High temperature
True/False
All state functions have exact differentials
True
What is the difference between ∆H and ∆U when 1.0
mol of grey tin (Sn, molar mass 118.7 g/mol, density
5.75 g/cm3) changes to white tin (density 7.31 g/cm3)
at 10 bar and 298 K?
-4.41 J
True/False
Standard state refers to a temperature of 298 K, with an undefined
pressure.
False Standard state implies pressure = 1 bar
Of these parameters, which are extensive variables
and which are intensive variables:
U, H, T, P, V, Cp, Cv
Extensive:
U, H, V, Cv, Cp
Intensive:
T, P
A cylinder of compressed natural gas has a volume of 20.0 L
and contains 1813 g of methane and 336 g of ethane.
Calculate the partial pressure of each gas at 22.0°C and the
total pressure in the cylinder.
pmethane =1.39 * 107 Pa
pethane = 1.34 * 106 Pa
True/False
The work done by a system in an adiabatic process equals to the system
internal energy change.
True
deltaU = w + q
For adiabatic q=0
Therefore deltaU = w
An ideal gas undergoes a two-step transition: first is
an isothermal reversible compression at 260 K from
(A) to (B), followed by a reversible expansion at
constant pressure to the original volume (C).
Calculate ∆H, ∆U, w, and q during this process. Note
heat capacity Cp,m = 37.1 J/K mol.
∆H = 10710 J
∆U = 8307 J
w = -1082 J
q = 9389 J
The above expression for the isobaric volumetric thermal expansion
coefficient can be rewritten as:
****Hint: for small x, ln(x) = 1-x
Given the following standard enthalpy of reaction
∆H°298 (kJ/mol)
-1170
-114
-72
find ∆H°298 for
∆H°298 = -414 kJ/mol
For alcohol oxidation to acetic acid,
C2H5OH(l) + O2(g) ⇒ CH3COOH(l) + H2O(l),
calculate the reaction enthalpy ∆rH° at 298K. What
about ∆rH° at 350 K, assuming Cp,m’s are
constant within this temperature range?
∆rH° at 298K = -492.5 kJ/mol
∆rH° at 298K = -89.49 kJ/mol
True/False
In a cyclic process, although the internal energy (U) and enthalpy (H) show no net
change, the work and heat are always nonzero.
False - U and H are state functions i.e. delta U and delta H are
path independent
W and q are path functions!