Question 1

Which of the following best describes the chemical potential ($$\mu_i) of a $$component in a mixture?

Accepted Answer

The contribution of that component to the total Gibbs energy of the mixture, per mole of the component.

Question 2

For an ideal binary gas mixture, what is the correct expression for the Gibbs energy of mixing ($$\$$Delta_{mix}$$G$$)?

Accepted Answer

$$\$$Delta_{mix}$$G = nRT(x_A \ln x_A + x_B \ln x_B)$$

Question 3

Which of the following statements about the entropy of mixing ($$\$$Delta_{mix}$$S) $$for ideal gases is correct?

Accepted Answer

$$\$$Delta_{mix}$$S is $$always positive for spontaneous mixing.

Question 4

Given 1.0 mol of gas A and 1.0 mol of gas B, each at 2.0 L, 1.0 bar, and 298 K, what is $$\$$Delta_{mix}$$G$$ when the partition is removed? ($$R = 8.314 \ J\ $$mol^{-1}$$K^{-1}$)

Accepted Answer

$$-3.4 kJ$$

Question 5

Which equation correctly relates the chemical potential of an ideal gas to its pressure?

Accepted Answer

$$\mu = \mu^\circ + RT \ln \left(\frac{p}{p^\circ}\right)$$

Question 6

For a mixture of 3.0 mol H$$_2 at$$ $$3p$$ and 1.0 mol N$$_2 at$$ $$p$$, what is the mole fraction and partial pressure of H$$_2$$ after mixing?

Accepted Answer

Mole fraction $$= \frac{3}{4}$$, partial pressure $$= \frac{3}{2}p$$

Question 7

Which of the following is true for the enthalpy of mixing ($$\$$Delta_{mix}$$H) $$for an ideal solution?

Accepted Answer

$$\$$Delta_{mix}$$H = 0$$

Question 8

Raoult’s Law states that the partial vapor pressure of component A in an ideal solution is:

Accepted Answer

$$p_A = x_A p_A^*$$

Question 9

Which of the following pairs of substances is most likely to form an ideal solution?

Accepted Answer

Benzene and toluene

Question 10

A solution is prepared by mixing 1.0 mol He, 3.0 mol Ne, 2.0 mol Ar, and 2.5 mol Xe at 298.15 K. What is $$\$$Delta_{mix}$$G$$? ($$R = 8.314 \ J\ $$mol^{-1}$$K^{-1}$)

Accepted Answer

$$-2.8 	imes 10^4$ J

Question 11

Which of the following best explains why ideal gases mix spontaneously?

Accepted Answer

The entropy of the system increases upon mixing.

Question 12

Which equation is used to calculate the change in chemical potential of an ideal gas with pressure at constant temperature?

Accepted Answer

$$d\mu = V_m dp$$

Question 13

For a binary mixture, the total Gibbs energy is given by:

Accepted Answer

$$G = n_A \mu_A + n_B \mu_B$$

Question 14

Which of the following is NOT an assumption of an ideal solution?

Accepted Answer

The intermolecular interactions between A and B are much stronger than A-A or B-B.

Question 15

Which law describes the relationship between the partial pressure of a component and its mole fraction in the liquid phase for an ideal solution?

Accepted Answer

Raoult’s Law

Question 16

If the mole fraction of component A in a binary ideal solution is 0.3, and $$p_A^* = 50$$ Torr, what is the partial vapor pressure of A?

Accepted Answer

$$15$$ 	ext{ Torr}$

Question 17

Which of the following is the correct expression for the entropy of mixing ($$\$$Delta_{mix}$$S) $$for an ideal binary mixture?

Accepted Answer

$$\$$Delta_{mix}$$S = -nR(x_A \ln x_A + x_B \ln x_B)$$

Question 18

Which of the following best describes the driving force for mixing in an ideal solution?

Accepted Answer

Increase in entropy

Question 19

In the context of phase equilibrium, what condition must be satisfied for two phases $$\alpha$$ and $$\beta to be in $$equilibrium?

Accepted Answer

$$\mu_i(\alpha, p, T) = \mu_i(\beta, p, T)$$

Thermodynamics of Simple Mixtures: Gibbs Energy, Mixing, and Raoult’s Law

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