CH 441 Exam 2 Conceptual Questions

Increases

A gas is slightly above its Boyle temperature. Do you expect z to increase or decrease as P increases? Above the Boyle temperature, Z _____ as P increases.

Critical, reduced, pressure, temperature

A system containing argon gas is at pressure P1 and temperature T1. How would you go about estimating the fugacity coefficient of the gas? Use the _____ constants of the gas to determined the _____ _____ and _____. The fugacity constant can then be estimated.

Is not, multiple, triple point

A triple point refers to a point in a P-T phase diagram for which three phases are in equilibrium. Do all triple points correspond to a gas-liquid-solid equilibrium? This _____ (is/is not) always the case due to the substances that have _____ solid phases and there can be a ____ ____ between 3 of these.

Pressures, volume, less, less

A van der Waals gas undergoes an isothermal reversible expansion under conditions such that z <1. Is the work done more or less than if the gas followed the ideal gas law? For a reversible expansion, the _____ are equal between real and ideal gases. However, by equation 7.6, _____ is _____ for a gas where z<1, and thus the work done is _____ than ideal.

Pressures, volume, greater

A van der Waals gas undergoes an isothermal reversible expansion under conditions such that z >1. Is the work done more or less than if the gas followed the ideal gas law? For a reversible expansion, the _____ are equal between real and ideal gases. However, by equation 7.6, _____ is greater for a gas where z>1, and thus the work done is _____.

Will not, indistinguishable, critical density, will not, liquid, evaporate, will, density, critical density

A vessel containing a liquid is opened inside an evacuated chamber. Will you see a liquid-gas interface if the volume of the initially evacuated chamber is (a) less than the critical volume, (b) much larger than the critical volume, and (c) slightly larger than the critical volume. (a) You _____ (will/will not) see an interface because liquid and gas are _____ above the ____ ____. (b) You _____ (will/will not) see an interface because all of the _____ will _____. (c) You _____ (will/will not) see an interface because the _____ is less than the ____ ____.

Are not, T, constant

Are the equations ΔG = ΔH - TΔS and ΔA = ΔU - TΔS applicable to all processes? These _____ (are/are not) applicable to all processes because ___ needs to be _____.

Higher, pressure, 1

As the pressure is increased at -45°C, ice 1 is converted to ice 2. Which of these phases has the lower density? Since the _____-density phase is more stable with increasing _____, Ice ___ is the less dense.

One substance, water, air, barometric, external, vapor

At a given temperature, a liquid can coexist with its gas at a single value of the pressure. However, you can sense the presence of H2O(g) above the surface of a lake by the humidity, and it is still there if the barometric pressure rises or falls at constant temperature. How is this possible? This statement holds for a system with only ____ ____. The system described has both _____ and _____. The change in _____ pressure is equivalent to an _____ pressure, which changes the _____ pressure only slightly.

Redlich-Kwong, pressure

Consider the comparison made between accurate results and those based on calculations using the van der Waals and Redlich-Kwong equations of state in Figures 7.1 and 7.5. Is it clear that one of these equations of state is better than the other under all conditions? The __________ equation gives more accurate results for almost all values of _____, but it is not necessarily better in all conditions.

Molecules, interact, pairwise interactions

Equation (1.20) states that the total pressure in a mixture of gases is equal to the sum of the partial pressures. Is this equation valid for real gases? If so, under what conditions? This is only valid if the _____ do not _____ with one another OR if all of the ____ ____ are equal for all of the gases.

Real, ideally, pressures, z, P, above, below

Explain the significance of the Boyle temperature. The Boyle temperature is the point at which _____ gases behave most _____ over a larger range of _____ compared to other temperatures. It also shows how ___ varies with ___ at low values of P. They are directly proportional _____ TB and inversely proportional _____ TB.

Composition, equilibrium, total composition, pressure

Explain the usefulness of a tie line on a P-Z phase diagram Tie lines allow for the _____ of the vapor and liquid phases in _____ to be determined for a given ____ ____ and _____.

Independent, temperature, pressure, mass

Explain why chemists doing quantitative work using liquid solutions prefer to express concentration in terms of molality rather than molarity. Molality is preferred because it is _____ of _____ and _____. While these quantities are not always conserved, _____ is.

P, V, no

Explain why the oscillations in the two-phase coexistence region using the Redlich-Kwong and van der Waals equations of state (see Figure 7.4) do not correspond to reality. The oscillations predict that ___ increases as ___ increases, and _____ real gas exhibits this behavior.

Repulsive, potential, intermolecular

For a given set of conditions, the fugacity of a gas is greater than the pressure. What does this tell you about the interaction between the molecules of the gas? If fugacity is greater than pressure, the _____ part of the _____ dominates the _____ interactions.

Is not, range, pressures, liquid, gas

For a pure substance, the liquid and gaseous phases can only coexist for a single value of the pressure at a given temperature. Is this also the case for an ideal solution of two volatile liquids? This _____ (is/is not) true because an ideal solution of two volatile liquids exist over a _____ of _____. This is only limited by pressures for which there is either barely any _____ or barely any _____.

Polar, intermolecular forces, low

For which substances is Trouton's rule a bad estimate and why? Trouton's rule is not good at estimating the ΔΗ for _____ substances because it does not account for ____ ____. These estimates are usually significantly _____.

Maximum

Fractional distillation of a particular binary liquid mixture leaves behind a liquid consisting of both components in which the composition does not change as the liquid is boiled off. Is this behavior characteristic of a maximum or a minimum boiling point azeotrope? This is characteristic of a _____ BP azeotrope.

Attractive interaction, surface, neighbors, force perpendicular, pressure increase

Give a molecular-level explanation as to why the surface tension of Hg(l) is not zero. Hg atoms have a strong ____ ____. The atoms at the _____ of the droplet have fewer _____ than those inside, and experience a net ____ ____ to the surface that leads to a ____ ____ inside the droplet.

Project, PT

How can you get a P-T phase diagram from a P-V-T phase diagram? You can _____ the PVT phase diagram onto the _____ plane.

Kx, pressure

If KP is independent of pressure, why does the degree of dissociation in the reaction Cl2 <-> 2Cl depend on pressure? Since dissociation depends on _____, and that depends on _____ by 6.76, then by extension, dissociation depends on pressure.

Squared

If you double the stoichiometric coefficients of a reaction, what happens to the Kp? The Kp would be _____ for the doubled reaction.

Unlikely, N2, diver, breathing

Is a whale likely to get the bends when it dives deep into the ocean and resurfaces? Answer this question by considering the likelihood of a diver getting the bends if he or she dives and resurfaces on one lung full of air as opposed to breathing air for a long time at the deepest point of the dive. The whale is _____ to get the bends on one lungful. This is because there is not enough _____ in a single lungful to cause the bends, but that is not the case for a _____ who is _____ at maximum depth.

Is, no

Is the equation (dU/dV)T = (αT-κTP)/κT valid for liquids, solids, and gases? This equation _____ (is/is not) valid because _____ assumptions were made when deriving this relationship.

<, <

Is the ratio of fugacity to pressure greater to or less than one if the attractive part of the interaction potential between gas molecules dominates? If attractive interactions dominate, then P___(</>)P(ideal), so f/P___(</>) 1.

H, 0, H

KP is independent of T for a particular reaction. What does this tell you about the reaction? If this is true, then ∆__r = ___, because dln(Kp)/dT is proportional to ∆__r

Does, triple point

Since dry ice sublimes, does it have a liquid phase? Dry ice _____ (does/does not). It sublimes at room temperature because the liquid phase exists above the ____ ____.

Increases

The value of the Boyle temperature _____ with the strength of the attractive interactions between molecules.

0

Under what conditions are Kp = Kχ? These two are equal when Δν = ___.

T, V, nonexpansion

Under what conditions does dA =< 0 define the spontaneity of a process? dA defines spontaneity when ___ and ___ are constant, and there is no _____ work.

T, P, nonexpansion

Under what conditions does dG =< 0 define the spontaneity of a process? dA defines spontaneity when ___ and ___ are constant, and there is no _____ work.

Moles, gaseous products, gaseous reactants

Under what conditions is the distribution of products in an ideal gas reaction system at equilibrium unaffected by an increase in the pressure? By equation 6.76, this distribution is unaffected if the number of _____ of ____ ____ equals the number of ____ ____.

Depth, intermolecular potential, distance, positive, reduced, normalized

Using the concept of the intermolecular potential, explain why two gases in corresponding states can be expected to have the same value for z. Different gases have different values for the _____ of ____ ____ and for the _____ at which this becomes _____. By using the _____ forms of P, V, and T, these differences are also _____.

Disordered, superfluid, liquid, gaseous, pure substance

Why does water have several different solid phases but only one liquid and one gaseous phase? Liquid and gaseous phases are _____, so that except in cases like a _____, it is impossible to distinguish between two _____ or _____ phases of the same ____ ____.

Pressure, G, small

Why is it reasonable to set the chemical potential of a pure liquid or solid substance equal to its standard state chemical potential at that temperature independent of the pressure in considering chemical equilibrium? It is reasonable to set μ* equal to μ at T independent of P because the _____ dependence of ___ is very _____ for solids and liquids.

-S, S, T, downward

Why is it reasonable to show the μ versus T segments for the three phases as straight lines as is done in Figure 8.1? More realistic curves would have some curvature. Is the curvature upward or downward on a μ versus T plot? Explain your answer. This is reasonable because the partial derivative (dμ/dT)P = __ ___. Because __ increases slowly with __, the real curves will be directed _____, but not rapidly.

Chemical potential, gas, steeply decreasing

Why is the magnitude of boiling point elevation less than that of freezing point depression? This is because the ____ ____ of the _____ is a more ____ ____ function (dμ=-Sm*dT). Also ΔHvap is much greater in magnitude than ΔHfus

Solvent, solute, solvent, solute, solute, neither

Why is the preferred standard state for the solvent in an ideal dilute solution the Raoult's law standard state? Why is the preferred standard state for the solute in an ideal dilute solution the Henry's law standard state? Is there a preferred standard state for the solution in which χsolvent = χsolute = 0.5? Raoult's Law defines the _____ because, when using it, the _____ has a weak effect on the _____. Henry's law describes the same for a _____ at low _____ concentration. __________ is adequate at χ = 0.5.

Fugacity, equal, pressure, low pressures

Why is the standard state of fugacity equal to the standard state of pressure? If this were not the case, the _____ would become _____ to the _____ in the limit of ____ ____.

State, path, initial, final

Why is ΔHsub,m = ΔHfus,m + ΔHvap,m? Because ΔH is a _____ function, it has the same value regardless of _____ as long as the _____ and _____ states are the same.

No, greater, greater

Will the fugacity coefficient of a gas above the Boyle temperature be less than one at low pressures? _____ (Yes/no). The integral in equation 7.21 is always _____ than zero, so γ is always _____ than one.

Minimum boiling point azeotrope, pure water

You boil an ethanol-benzene mixture with χethanol = 0.35. What is the composition of the vapor phase that first appears? What is the composition of the last liquid left in the vessel? To find this, look at the ____ ____ ____ ____ of the mixture in a reference table. The last liquid remaining is ____ ____.

Greater, less

You have calculated the pressure exerted by ethane using the ideal gas law and the Redlich-Kwong equations of state. How do you decide if the repulsive or attractive part of the molecular potential dominates under the given conditions? Repulsion dominates if the RK pressure is _____ than ideal pressure. Attraction dominates if the RK pressure is _____ than the ideal pressure.

Is not, <, endo, increases, above

Consider a gas phase reaction where Δμ(T) = 15.5 kJ/mol and ΔHr = 21 kJ/mol at 350 K. Is the reaction spontaneous at 350 K? The reaction _____ (is/is not) spontaneous at 350 K because spontaneity requires that Δμ __ (>/<) 0. Is the reaction is spontaneous at temperatures well below 350 K? Since the reaction is ____thermic, KP _____ as T increases. Therefore, the reaction is only spontaneous at temperatures _____ 350K.

Less, higher, lower

By invoking the pressure dependence of chemical potential μ, show that if a valve separating a vessel of pure A from a vessel containing a mixture of both A and B is opened, mixing will occur. Both A and B are ideal gases at 1 bar. Since μA (T,P) = μA0 (T) + RTln(PA/P0), the chemical potential of A in the mixture is _____ than in the pure gas. Because mass flows from areas of _____ to _____ μ, mixture will occur.

Greater, O2

By looking at the a and b values for the van der Waals equation of state, decide whether 1 mole of O2 or H2O has the higher pressure at the same value of T and V. a is significantly larger for H2O. Therefore, the attractive forces between H2O molecules are _____ than O2. As a result, _____ has the greater pressure.

Gas, liquid, equilibrium, volumes, temperature

Why does the triple point in a PT diagram become a triple line in a PV diagram? This is the case because the _____ and _____ are in _____ for a range of _____ at a given _____.

G, negative, S, H

The entropy of two liquids is lowered if they mix. How can immiscibility be explained in terms of thermodynamic state functions? Since ΔG = ΔΗ - ΤΔS, it is possible for Δ___ to be _____ even if Δ___ is positive if Δ___>TΔS.

Equal

The reaction A + B --> C + D is at equilibrium for ξ=0.5. What does this tell you about the ΔGf for reactants and products? They are _____.

Reactants, lower, products

The reaction A+B --> C +D is at equilibrium for ξ=0.1. What does that tell you about the ΔGf of reactants and products? Because ξ = 0.1, the _____ are favored. Since they are favored, their ΔGf value is likely to be _____ than the _____.

Non-uniform, contaminated

What can you say about the composition of the solid below the eutectic temperature in Figure 9.26 on a microscopic scale? Below Te, the solid is ____-____ and crystallites are _____.

Rises, far, rises sharply, falls, falls sharply, same density

What can you say about the density of liquid and gaseous water as the pressure approaches the critical value from lower (gas) and higher (liquid) values? Assume that the temperature is constant at the critical value. The density of the gas _____ slowly with temperature _____ from the Pc, but ____ ____ when approaching Pc. The density of the liquid _____ slowly while far from Pc but ____ ____ when approaching it. At Pc, they have the ____ ____.

Decreases slowly, decreases sharply, 0

What can you say about ΔΗvap of a liquid as T approaches Tc? ΔHvap ____ ____ while far from Tc but ____ ____ as T approaches Tc, where it has the value ___.

Cohesive force, liquid, minimizes, surface area, pressure

What is the physical origin of the pressure difference across a curved liquid-gas interface? The origin is the ____ ____ of the _____, which is not zero in magnitude. If the interface is curved, this _____ the ____ ____, leading to a _____ difference.

Intermolecular interactions, argon, electrons, polarizable

Which of Ne or Ar has the larger van der Waals parameter a? Explain your reasoning. Since the a parameter depends on ____ ____, _____ has the larger a value because it has more _____ and is therefore more _____.

Size, argon

Which of Ne or Ar has the larger van der Waals parameter b? Explain your reasoning. The b parameter depends on the _____ of the atoms, so _____ has a larger b value.

G, G, nonexpansion

Which thermodynamic state function gives a measure of the maximum electrical work that can be carried out in a fuel cell? Δ___ is the state function because d___ <= dw_____

Freezing point, slightly, pressure

Why are the triple point temperature and the normal freezing point very close in temperature for most substances? This is because the ____ ____ changes very _____ with _____.

Phase rule, 4

Why are there no points in the phase diagram for sulfur in Figure 8.11 that show rhombic and monoclinic solid phases in equilibrium with liquid and gaseous sulfur? According to the ____ ____, it is impossible for ___ phases to exist in equilibrium.

Dilution, solute, vapor pressure, evaporation, condensation, identity, surface, concentration

Why do colligative properties depend only on solute concentration and not the identity of the solute? Colligative properties exist because the _____ of the _____ lowers the ____ ____, which effects the rates of _____ and _____. The _____ of the solute does not affect its likelihood of being near the _____, but the _____ does.

Inverse, Cpm

Why do the temperature versus heat curves in the solid, liquid, and gas regions of Figure 8.7 have different slopes? The slopes of these curves are equal to the _____ of _____, which has a different value for each phase.

Liquid, gas, density, distinguished, beyond

Why does the liquid-gas coexistence curve in a P-T phase diagram end at the critical point? At the critical point, the _____ and the _____ have the same _____, and can no longer be _____. This is also true of all points on the curve _____ that point.