Mixtures - thermo

Question 1

What is a mole fraction?

Answer 1

Number of moles of a species divided by the total number of moles of all species

Question 2

What is the equation for mole fraction?

Answer 2

Xa = na / n

Question 3

What is Dalton’s law?

Answer 3

The partial pressure of a gas in a mixture is the mole fraction times the total pressure

Question 4

What is the equation for Dalton’s law?

Answer 4

Pa = XaP

Question 5

Which equation did Dalton’s law originate from?

Answer 5

Ideal gas equation

pV = nRT

Question 6

What is not taken into account in Dalton’s law?

Answer 6

The type of species

Question 7

What are the three steps to use pV = nRT for Daltons equation?

Answer 7

Split it up into its parts
Add the two parts together
Take the ratios

Question 8

What is the final equation from pV = nRT? What is this the same as?

Answer 8

Pa / p = Xa

Rearranged Dalton’s law

Question 9

All gases are miscible, what does this mean?

Answer 9

They are all able to be mixed

Question 10

What is the driving force for all gases being miscible?

Answer 10

A mixture is always more disordered than the pure substances

Question 11

Is the change in entropy positive or negative?

Answer 11

Always positive

Question 12

What is the value of Xa always?

Answer 12

Bigger than 0

Less than 1

Question 13

What is the value of ln Xa always?

Answer 13

Less than 0

Question 14

What is the equation for entropy of mixing?

Answer 14

ΔS = -nR (xA lnxA + xB lnxB)

Question 15

Is there heat involved in the mixing of gases?

Answer 15

No

Question 16

What is Raoult’s law?

Answer 16

The partial vapour pressure of a solvent in a mixture is proportional to its mole fraction in the solution and its vapour pressure when pure

Question 17

What is the equation for Raoult’s Law?

Answer 17

Pa = xAP*a

Question 18

What is P*a?

Answer 18

The vapour pressure of pure A

Question 19

When is Raoult’s law good to use?

Answer 19

When the two liquids are similar

Question 20

When does the approximation of Raoult’s law become poor?

Answer 20

When there are strong forces between the molecules used

Question 21

What are solutions that obey Raoult’s law called?

Answer 21

Ideal solutions

Question 22

What is the solvent in raoult’s law?

Answer 22

The liquid that is in excess

Question 23

What is easiest to measure for Raoult’s law?

Answer 23

The pressure of the vapour that is in equilibrium with the liquid

Question 24

What is Henry’s law?

Answer 24

The partial vapour pressure of a solute in a solution is proportional to it’s mole fraction

Question 25

When is Henry's law used?

Answer 25

When looking at the solute

Question 26

What is the equation for Henry's law?

Answer 26

Pb = xBKB

Question 27

What is an ideal-dilute solution?

Answer 27

Dilute solutions where the solute obeys Henry's law and the solvent obeys Raoult's law

Question 28

What are the axes for the graphs for Raoult's law and Henry's law?

Answer 28

``` Y = pressure X = mole fraction ```

Question 29

In the graph for Raoult's law, what are the three lines?

Answer 29

Total pressure Partial pressure of A Partial pressure of B

Question 30

When is Raoult's law good for looking at mole fractions and pressure?

Answer 30

When mole fraction is near 1 | That is when it is nearest the actual pressure

Question 31

When is Henry's law good for looking at mole fractions and pressure?

Answer 31

When mole fraction is near 0 | That is when it is nearest the actual pressure

Question 32

What is the equation for Lever's rule?

Answer 32

n'l' = n''l''

Question 33

What does Lever's rule equation mean?

Answer 33

the number of moles of 1 x length of tieline on that side = the number of moles of 2 x length of tieline on the other side

Question 34

What does the Lever rule give you?

Answer 34

The amounts of liquid and vapour

Question 35

What is a tie-line?

Answer 35

Horizontal line between the curve representing the liquid composition and that representing the vapour composition at the same temperature

Question 36

What is Lever's rule used for?

Answer 36

Calculating the amount of each phase in a mixture

Question 37

In a diagram for Lever's rule, what is below the bottom curve?

Answer 37

Liquid phase

Question 38

In a diagram for Lever's rule, what is above the top curve?

Answer 38

Vapour phase

Question 39

In a diagram for Lever's rule, what is in between the two curves?

Answer 39

Equilibrium

Question 40

What is an azeotrope?

Answer 40

Mixture of two liquids which has a constant boiling point and composition during distillation

Question 41

How does an azeotrope behave?

Answer 41

As if it were a pure substance

Question 42

How can the graphs be used for fractional distillation?

Answer 42

Raise temperature to where A would be just above the bottom curve to create an equilibrium between liquid and vapour and remove the small amount of vapour Repeat until you end up with pure B

Question 43

What is an eutectic mixture?

Answer 43

A mixture with the lowest boiling point

Question 44

What is the eutectic point?

Answer 44

The point where the liquids freeze