The atmosphere of the planet Venus is almost entirely composed
of carbon dioxide (about 96.5% carbon dioxide). The carbon
dioxide on Venus could be in equilibrium with carbonate ions in
minerals on the planet's crust. Two possible equilibrium systems
involve CaSio3 and MgSiO3:
The first graph that follows shows the expected pressures of
carbon dioxide (in atm) at different temperatures for each of
these equilibrium systems. (Note that both axes on this graph
are logarithmic.) The second graph is a phase diagram for carbon
dioxide. Examine the graphs and answer the questions.
a. The partial pressure of carbon dioxide on the surface of Venus
is 91 atm. What is the value of the equilibrium constant (Kp)
if the Venusian carbon dioxide is in equilibrium according to
system 1? According to system 2?
b. The approximate temperature on the surface of Venus is about
740 K. What is the approximate carbon dioxide concentration
for system 1 at this temperature? For system 2? (Use a point at
approximately the middle of each colored band, which
represents the range of possible values, to estimate the carbon
dioxide concentration.)
c. Use the partial pressure of carbon dioxide on the surface of
Venus given in part a to determine which of the two equilibrium
systems is more likely to be responsible for the carbon
dioxide on the surface of Venus.
d. From the carbon dioxide phase diagram, determine the minimum
pressure required for supercritical carbon dioxide to
form. If the partial pressure of carbon dioxide on the surface
of Venus was higher in the distant past, could supercritical
carbon dioxide have existed on the surface of Venus?