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Advanced Higher Chemistry: Unit 1- Inorganic And Physical Chemistry > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

What do chemical reactions take place as a result of?

A

bond breaking and bond making reactions

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2
Q

What kind of reaction is bond breaking?

A

endothermic

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3
Q

What kind of reaction is bond making?

A

exothermic

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4
Q

What is thermochemistry the study of?

A

the study of energy changes during chemical reactions, measured in kJ mol-1

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5
Q

What are energy changes measured in terms of?

A

enthalpy changes (or changes in energy contents)

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6
Q

What does a change in energy content result in?

A

a change in temperature of the surroundings

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7
Q

What do total enthalpy changes always refer to?

A

the system and the surroundings

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8
Q

What can the system be regarded as?

A

the part of the world we are investigating e.g. a chemical reaction

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9
Q

What are the surroundings regarded as?

A

the rest of the world e.g. the air surroundings the reaction vessel, or water the reaction is taking place in.

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10
Q

What is important to remember about the total amount of energy during a chemical reaction?

A

The total amount of energy is unchanged during a chemical reaction - energy may be exchanged between the materials and the surroundings, but the total amount of energy of the materials and surroundings remains constant

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11
Q

What is the first law of thermodynamics?

A

energy can neither be created nor destroyed, but can be changed from one form to another

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12
Q

State Hess’s law.

A

The enthalpy change for a reaction is the same regardless of the route taken

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13
Q

What are the standard conditions for temp and pressure?

A

298K (25’c) and 1 atmosphere respectively (STP)

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14
Q

What are substances said to be?

A

in their standard state, i.e. their normal physical states under standard conditions

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15
Q

What concentration are solutions at in their standard state?

A

1 mol l-1

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16
Q

What are enthalpy changes measured under standard conditions known as? What symbol is used?

A

a standard enthalpy change delta H’

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17
Q

What is the enthalpy of formation?

A

the enthalpy change when 1 mole of a substance is formed for its elements under standard conditions.

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18
Q

What is the standard enthalpy of formation of an element?

A

0

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19
Q

How can the standard enthalpy of a reaction being calculated?

A

using standard enthalpies of formation

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20
Q

Define entropy.

A

A term which refers to the chaos or disorder in a system, and measure of chaotic dispersal of energy and matter.

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21
Q

The greater the disorder in a system, the…

A

greater the entropy

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22
Q

Describe the effect of temperature on entropy.

A

Entropy increases as temperature increases

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23
Q

What is the standard molar entropy, S*?

A

the entropy content of one mole of a substance, under standard conditions

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24
Q

What are the units of entropy?

A

JK-1 mol-1

25
Q

What does the third law of thermodynamics state?

A

the entropy of a perfect crystal at 0K is zero

26
Q

What does the crystal lattice at absolute zero have?

A

perfect order and therefore no entropy i.e. the particles are not in motion

27
Q

What happens as a solid is heated?

A

the particles gain KE and entropy slowly increases

28
Q

Describe the entropy increase between solid, liquid and gas.

A

The entropy increase from liquid to gas is greater than that from solid to liquid

29
Q

What do changes in state involve?

A

changes in entropy

30
Q

For any spontaneous process describe what happens to the total entropy of the system and its surroundings.

A

increases

31
Q

What is a spontaneous process?

A

one that can take place on its own irrespective of how long it takes

32
Q

What are spontaneous exothermic reactions driven by?

A

the large increase in entropy they generate in the surroundings

33
Q

How is the entropy of surroundings calculated.

A

calculated from the standard enthalpy change for the reaction and temperature, T, in Kelvin.

34
Q

What are spontaneous endothermic reactions driven by?

A

the large increase entropy they generate in the system i.e. the reaction mixture itself

35
Q

For a spontaneous endothermic reaction explain what happens to the entropy of the surroundings.

A

Heat is absorbed from the surroundings - decreases the entropy of the surroundings

36
Q

What does the spontaneity of a reaction involve?

A

two thermodynamic quantities, enthalpy and entropy

37
Q

What are the favourable conditions for a spontaneous reaction?

A

/\H < 0

/\S > 0

38
Q

What are the favourable conditions for a non-spontaneous reaction?

A

/\H > 0

/\S < 0

39
Q

In order to determine whether a reaction is spontaneous what other thermodynamic quantity is used?

A

Gibbs Free Energy /\G

40
Q

What is the unit of /\G?

A

J mol-1

41
Q

For a spontaneous reaction, what will /\G always be?

A

negative

42
Q

What is the equation to calculate /\G? Include the units

A 
/\G= /\H - T/\S
/\G is Gibbs Free Energy in kJ
/\H is the enthalpy change in kJ mol-1
T is the temperature in Kelvin (+273)
/\S is the entropy change in JK-1 mol-1
43
Q

For a non-spontaneous reaction, what will /\G always be?

A

positive

44
Q

What equation can be used to calculate standard free energy changes?

A

/\G= {sigma}/\Gproducts - {sigma}/\Greactants

45
Q

If /\G is negative, what will the reaction proceed at?

A

any temperature

46
Q

In terms of the reaction what will happen if /\G is positive?

A

the reaction will not proceed

47
Q

What is the temperature at which the reaction becomes feasible?

A

the CRITICAL TEMPERATURE

48
Q

At the critical temperature, what is the value of /\G?

A

0

49
Q

What equation is used to calculate the temp at which the reaction becomes feasible?

A

T= /\h//\S

50
Q

At chemical equilibrium what is the Gibbs free energy value?

A

At a minimum

51
Q

If /\G is <0 what does this suggest about the forward reaction?

A

it is feasible so [products]>[reactants] Equilibrium lies to the RHS and therefore K>1

52
Q

If /\G is >0 what does this suggest about the reverse reaction?

A

it is feasible so [reactant]>[products]

Equilibrium lies to the LHS and therefore K<1

53
Q

If /\G is equal to zero what is the value of K?

A

1

54
Q

What does the value of /\G for a reaction not predict?

A

the rate of the reaction

55
Q

What may a reaction have that prevents it from taking place?

A

A reaction may have a negative /\G but have a high activation energy

56
Q

In a closed system what must the /\Ssystem be?

A

positive

57
Q

If /\S is -ve what does this suggest about how disordered the reactants and products are?

A

[reactants]>[products]

58
Q

If /\S is +ve what does this suggest about how disordered the reactants and products are?

A

[products]>[reactants]

Advanced Higher Chemistry: Unit 1- Inorganic And Physical Chemistry (12 decks)

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