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CHY1201 - Elements of physical chemistry > Mixtures - thermo > Flashcards

Mixtures - thermo Flashcards

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1
Q

What is a mole fraction?

A

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

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2
Q

What is the equation for mole fraction?

A

Xa = na / n

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3
Q

What is Dalton’s law?

A

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

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4
Q

What is the equation for Dalton’s law?

A

Pa = XaP

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5
Q

Which equation did Dalton’s law originate from?

A

Ideal gas equation

pV = nRT

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6
Q

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

A

The type of species

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7
Q

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

A

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

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8
Q

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

A

Pa / p = Xa

Rearranged Dalton’s law

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9
Q

All gases are miscible, what does this mean?

A

They are all able to be mixed

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10
Q

What is the driving force for all gases being miscible?

A

A mixture is always more disordered than the pure substances

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11
Q

Is the change in entropy positive or negative?

A

Always positive

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12
Q

What is the value of Xa always?

A

Bigger than 0

Less than 1

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13
Q

What is the value of ln Xa always?

A

Less than 0

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14
Q

What is the equation for entropy of mixing?

A

ΔS = -nR (xA lnxA + xB lnxB)

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15
Q

Is there heat involved in the mixing of gases?

A

No

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16
Q

What is Raoult’s law?

A

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

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17
Q

What is the equation for Raoult’s Law?

A

Pa = xAP*a

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18
Q

What is P*a?

A

The vapour pressure of pure A

19
Q

When is Raoult’s law good to use?

A

When the two liquids are similar

20
Q

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

A

When there are strong forces between the molecules used

21
Q

What are solutions that obey Raoult’s law called?

A

Ideal solutions

22
Q

What is the solvent in raoult’s law?

A

The liquid that is in excess

23
Q

What is easiest to measure for Raoult’s law?

A

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

24
Q

What is Henry’s law?

A

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

25
Q

When is Henry’s law used?

A

When looking at the solute

26
Q

What is the equation for Henry’s law?

A

Pb = xBKB

27
Q

What is an ideal-dilute solution?

A

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

28
Q

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

A 
Y = pressure 
X = mole fraction
29
Q

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

A

Total pressure
Partial pressure of A
Partial pressure of B

30
Q

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

A

When mole fraction is near 1

That is when it is nearest the actual pressure

31
Q

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

A

When mole fraction is near 0

That is when it is nearest the actual pressure

32
Q

What is the equation for Lever’s rule?

A

n’l’ = n’‘l’’

33
Q

What does Lever’s rule equation mean?

A

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

34
Q

What does the Lever rule give you?

A

The amounts of liquid and vapour

35
Q

What is a tie-line?

A

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

36
Q

What is Lever’s rule used for?

A

Calculating the amount of each phase in a mixture

37
Q

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

A

Liquid phase

38
Q

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

A

Vapour phase

39
Q

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

A

Equilibrium

40
Q

What is an azeotrope?

A

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

41
Q

How does an azeotrope behave?

A

As if it were a pure substance

42
Q

How can the graphs be used for fractional distillation?

A

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

43
Q

What is an eutectic mixture?

A

A mixture with the lowest boiling point

44
Q

What is the eutectic point?

A

The point where the liquids freeze

CHY1201 - Elements of physical chemistry (28 decks)

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