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A-Level Chemistry > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

What is enthalpy change?

A

It is the heat energy transferred in a reaction at constant pressure.

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2
Q

What is enthalpy of formation?

A

It is the enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions.

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3
Q

What is the enthalpy change of atomisation of an element?

A

It is the enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state.

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4
Q

What is the first ionisation energy?

A

It is the enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms.

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5
Q

What is the first electron affinity?

A

It is the enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms.

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6
Q

What is the enthalpy change of hydration?

A

It is the enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions.

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7
Q

What is the bond dissociation enthalpy?

A

It is the enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken.

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8
Q

What is the enthalpy change of atomisation of a compound?

A

It is the enthalpy change when 1 mole of a compound in its standard state is converted into gaseous atoms.

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9
Q

What is the second ionisation energy?

A

It is the enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions.

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10
Q

What is the second electron affinity?

A

It is the enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions.

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11
Q

What is the enthalpy of solution?

A

It is the enthalpy change when 1 mole of solute is dissolved in enough solvent that no further enthalpy change occurs on further dilution.

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12
Q

What is lattice enthalpy?

A

It is a measure of ionic bond strength

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13
Q

What is lattice enthalpy of formation?

A

It is the enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions.

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14
Q

What is the lattice enthalpy of dissociation?

A

It is the enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions under standard conditions.

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15
Q

What is the enthalpy of combustion?

A

It is the enthalpy change when 1 mole of a substance is completely burnt in oxygen with all the reactants and products in their standard states under standard conditions.

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16
Q

What is the enthalpy of neutralisation?

A

It is the enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions.

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17
Q

What is the enthalpy of vaporisation?

A

It is the enthalpy change when 1 mole of a liquid is turned into a gas.

18
Q

What is the enthalpy of fusion?

A

It is the enthalpy change when 1 mole of a solid is turned into a liquid.

19
Q

What is Hess’ Law?

A

The enthalpy change for a reaction is independent of the route taken

20
Q

Which factors affect lattice enthalpies?

A

The size of the ions

The charges on the ions

21
Q

How does size affect the lattice enthalpy?

A

The larger the ions, the less negative the enthalpies of lattice formation. The charges are further apart, therefore, there is a weaker force of attraction between them.

22
Q

How do charges on the ions affect the lattice enthalpy?

A

The larger the charge on the ion, the greater the attraction between the ions, therefore, the stronger the lattice enthalpy.

23
Q

What are the assumptions of theoretical lattice enthalpies?

A

The assumptions are of a perfect ionic model

  • the ions are 100% ionic
  • the ions are spherical
  • the attractions are purely electrostatic
24
Q

Why are the theoretical and experimental values different?

A

This is evidence that the ionic compounds have some covalent character. The positive ions polarise the neighbouring negative ions.

25
Q

What type of reaction is the lattice enthalpy of dissociation and why?

A

The bonds between the ions break to give free ions

26
Q

What type of reaction is the enthalpy change of hydration and why?

A

Exothermic

Bonds between the ions and the water are made

27
Q

Why can water molecules bond to the ions?

A

Oxygen is more electronegative than hydrogen, and therefore draws electrons towards itself, creating a dipole. The dipole means that the positively charged hydrogen atoms can form bonds with negative ions and the negatively charged oxygen can form bonds with positive ions.

28
Q

When do substances generally dissolve?

A

If the energy released is roughly the same or greater than the energy taken in.

29
Q

What is entropy?

A

It is a measure of the number of ways that particles can be arranged and the number of ways that the energy can be shared out between the particles.

30
Q

What is the effect of change in physical state on the entropy?

A

Solids have the lowest entropy because the particles vibrate about fixed points.
Gases have the highest entropy because the particles move around rapidly and randomly.

31
Q

What is the effect of having more particles on the entropy?

A

The more particles there are, the more ways there are for them and their energy to be arranged

32
Q

How does temperature affect entropy?

A

The higher the temperature, the faster the particles vibrate/move and so the greater the entropy.

33
Q

Why is the entropy increase from liquid to gas greater than the increase from solids to liquids?

A

There is a large amount of disorder in gases compared to solids and liquids.

34
Q

How do you calculate entropy(S) change?

A

change in S = S(products) - S(reactants)

35
Q

What is free energy change(G)?

A

It is a measure used to predict whether a reaction is feasible/spontaneous.

36
Q

What is the condition for a reaction to be feasible?

A

change in G must be negative or zero

37
Q

Why might a reaction not happen or be so slow even if it is feasible?

A

The reaction might have a high activation energy

38
Q

How can change in G be calculated?

A

change in G(J/mol) = enthalpy change(J/mol) - temperature(K)*entropy change(J/K/mol)

39
Q

What is G when the reaction is exothermic and has a positive entropy change?

A

change in G is always negative

The reactions are feasible at any temperature

40
Q

What is G when the reaction is endothermic and has a negative entropy change?

A

change in G is always positive

The reactions are not feasible at any temperature

41
Q

How do you calculate the temperature at which the reaction is just feasible?

A

T= enthalpy change/entropy change

42
Q

What is the standard entropy of a substance?

A

It is the entropy of 1 mole of that substance under standard conditions.

A-Level Chemistry (30 decks)

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