Lecture 5 (8)

#3 Why is ΔHmix = 0 for ideal gases?

• There are no bonds at all between ideal gas molecules

• Ideal gases do not mix

• Mixing of ideal gases is always adiabatic

• The partial molar volume of ideal gases is equal to zero.

#4 If the derivative of the chemical potential with respect to pressure is smaller for a real gas than for an ideal gas,

• the chemical potential of the real gas is smaller than that of the ideal gas. There are no bonds at all between ideal gas molecules.

• the compression factor is larger than 1.

• the real gas will condense at higher temperature than the ideal gas.

• the molar volume of the real gas is smaller than the molar volume of the ideal gas.

#5 Which proposition is false?

• There are no interactions in an ideal gas.

• In a real gas at high p repulsive forces are dominant.

• There are no interactions in an ideal solution.

• In a real solution with A and B clusters may form.

#6 What is Raoult’s law?

• x_B = x_A

• p_B = p_A

• p_B = x_B p_B*

• p_B = x_A p_B*

#7 What is true?

• p_B* > p_A*

• p_B* < p_A*

#8 Which proposition is correct?

• p_B* > p_A*

• k_^A < p_A*

• k_B > k_A

• k_A > p_A*

#9 What is the partial pressure of A ideal-diluted in B (xA=0.01, pA*=6000 Pa, kA=100.000 Pa)?

• p_A = 6000 Pa

• p_A = 1000 Pa

• p_A = 60 Pa

• p_A = 1060 Pa

#10 Which law describes the partial pressure of substance 2 for an ideal-dilute/ideal solution?

• p₂ = x₂ p₂* for small x and p₂ = x₂ k₂ for x close to 1.

• p₂ = x₂ k₂ for small x and p₂ = x₂ p* for x close to 1.

• p₂ = x₂ k₂ for all x ∈ [0,1]

• p₂ = x₂ p* for all x ∈ [0,1]

#11 What was the assumption for deriving the boiling point elevation?

• ΔH_mix > 0

• ΔH_mix < 0

• T_b(solute) >> T_b(solvent)

• T_b(solute) = T_b(solvent)

#12 Why is salt put on icy roads?

• For aesthetical reasons: Ice does not look nice.

• Because the ice melts due to the dissociation heat.

• Because salt does not mix with ice but with water.

• Because the increase in entropy leads to heat output.