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chemistry > Thermodynamics Part 2 > Flashcards

Thermodynamics Part 2 Flashcards

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1
Q

What is entropy a measure of

A

Disorder in a system

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2
Q

Symbol for entropy

A

S

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3
Q

Why are the values for entropy always positive

A

Particles always have energy

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4
Q

Units of entropy

A

JK-1mol-1

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5
Q

What needs to be done when combining entropy with enthalpy

A

/1000

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6
Q

Factors which determine the entropy of a substance

A
  • state of matter
  • dissolving
  • mixtures
  • number of particles
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7
Q

What is the entropy trend in state of matter and why

A

Entropy increases solid>liquid>gas as they’re more disordered

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8
Q

Trend in dissolving solid + solvent> solution

A

Entropy increases

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9
Q

Trend in entropy in formation of mixtures

A

Entropy increases

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10
Q

Trend in entropy as number of particles increases

A

Entropy increases

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11
Q

How to calculate delta S

A

Sum of S(prods) - Sum of S(reacts)

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12
Q

Effect of temperature on entropy: entropy is zero at 0K as

A

The particles have no kinetic energy therefore no movement

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13
Q

Effect of temperature on entropy: why does entropy increase as temperature increases

A

Particles move more and become more disordered

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14
Q

Effect of temperature on entropy: why is the second increase in entropy much bigger than the first

A

Gas particles have far more disorder than liquid therefore the entropy change from liquid to gas if much greater than solid to liquid

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15
Q

What can the values for entropy change be despite S values always being positive

A

Either positive or negative

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16
Q

When is Delta S positive

A

When there is an increase in disorder

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17
Q

Examples of positive delta S

A
  • dissolving
  • increase in number of moles of gas
  • melting
  • boiling
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18
Q

Why is delta S positive when dissolving occurs

A

The solution is more disordered than the solvent and solute

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19
Q

Why is delta S positive when there is an increase in the number of miles of gas

A

More moles of gas are more disordered

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20
Q

When is delta S positive when melting occurs

A

Liquids are more disordered than solids

21
Q

Why is delta S positive when boiling occurs

A

Gases are much more disordered than liquids

22
Q

What is a positive delta S favourable in terms of

A

Entropy

23
Q

When is delta S negative

A

When there is a decrease in disorder

24
Q

Examples of negative delta S

A
  • precipitation
  • decrease in number of moles of gas
  • freezing
  • condensing
25
Q

Why is delta S negative in precipitation reactions

A

The solid is less disordered than the aqueous ions

26
Q

Why is delta s negative when there’s a decrease in the number of moles of gas

A

Less moles of gas are less disordered

27
Q

Why is delta s negative when freezing occurs

A

Solids are led disordered than liquids

28
Q

Why is delta s negative when condensing occurs

A

Liquids are much less disordered than gases

29
Q

What is a negative delta unfavourable in terms of

A

Entropy

30
Q

Units of enthalpy change

A

kJmol-1

31
Q

What is delta H in an exothermic reaction

A

Negative

32
Q

When is a negative delta H favourable in terms of

A

Enthalpy change

33
Q

What is delta h in an endothermic reaction

A

Positive

34
Q

What is a positive delta h unfavourable in terms of

A

Enthalpy change

35
Q

How to calculate delta H for a reaction

A

Sum of delta H products - sum of delta H reactants

36
Q

What three factors contribute to whether a reaction will be feasible at a given temperature

A

Temperature
Entropy change
Enthalpy change

37
Q

What do the 3 factors that contribute to whether a reaction is feasible at given temperature combine to give

A

A new quantity called the Gibbs free energy change

38
Q

Gibbs free energy change

A

Delta G = delta H- T delta S

39
Q

What must delta G be for a reaction to be feasible

A

Zero or negative

40
Q

Why must delta s be converted to kJK-1mol-1

A

The units of Delta g and delta H are kJmol-1

41
Q

Does the sign of delta G tell us anything about the rate of a reaction

A

No, it only tells us whether a reaction is thermodynamically feasible

42
Q

When may a reaction not happen even if it is thermodynamically feasible

A

If the activation energy is too high

43
Q

Why am endothermic reaction can take place spontaneously at room temp: when does a spontaneous process oroceed

A

When delta g is less than or equal to 0

44
Q

Why am endothermic reaction can take place spontaneously at room temp: what does TdeltaS have to be greater than for a reaction to be spontaneous at room temp

A

Delta H

45
Q

Why can a relation with a negative (unfavourable) entropy change be feasible at room temperature

A

Even though delta S is negative, delta H is also negative

46
Q

Formula relating the calculation of temperature at which a reaction becomes feasible

A

T= deltaH/deltaS

47
Q

What do free energy graphs show

A

The relationship between free energy and temperature

48
Q

What can free energy graphs be used to find

A

The temperature at which a reaction becomes feasible

49
Q

What equation can we use for free energy graphs and why

A

The plot is always a straight line

Y=mx+c

chemistry (42 decks)

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