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chemistry > module 5: physical chemistry and transition elements > Flashcards

module 5: physical chemistry and transition elements Flashcards

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1
Q

what is lattice enthalpy?

A

the enthalpy change when one mole of an ionic compound is formed from its gaseous ions, under standard conditions

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2
Q

is the value for lattice enthalpy change always positive or negative, and why?

A

negative, lattice enthalpy involves ionic bond formation from separate gaseous ions which is an exothermic change

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3
Q

what are the key features about lattice enthalpy?

A
  • lattice enthalpy is an exothermic change, lattice enthalpies have a negative sign because energy is given out when ionic bonds are being formed from gaseous ions
  • lattice enthalpy is a measure of the strength of ionic bonding in a giant ionic lattice, a large negative value shows that there are strong electrostatic forces of attraction between the oppositely charged ions in the lattice
  • a covalent substance does not have a lattice enthalpy because there are no ions in its structure
  • lattice enthalpies cannot be measure directly because it is impossible to form a mole of an ionic lattice from gaseous ions
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4
Q

how are lattice enthalpies calculated indirectly?

A

Born-Haber cycle

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5
Q

what is the standard enthalpy change of atomisation?

A

the enthalpy change when one mole of gaseous atoms are formed from the element in its standard state under standard conditions

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6
Q

why is the standard enthalpy change of atomisation always an endothermic process?

A

energy is taken in for bond breaking to form gaseous atoms

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7
Q

what is the difference between electron affinity and ionisation energy?

A

electron affinity is the opposite of ionisation energy
- electron affinity measures the energy to gain electrons
- ionisation energy measures the energy to lose electrons

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8
Q

what is the first electron affinity?

A

the enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

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9
Q

why can lattice enthalpies not be determined directly?

A

you cannot form one mole of an ionic lattice from gaseous ions

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10
Q

what are the equations for making the solid sodium chloride?

A
  • atomisation of sodium
  • atomisation of chlorine
  • ionisation of sodium
  • electron affinity of chlorine
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11
Q

what is the standard enthalpy change of formation?

A

the enthalpy change when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states

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12
Q

what is the standard enthalpy change of atomisation?

A

the enthalpy change when one mole of gaseous atoms is formed from the element in its standard state under standard conditions

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13
Q

what is the first ionisation energy?

A

the enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

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14
Q

what is the first electron affinity?

A

the enthalpy change when one electron is added to one mole of gaseous atoms to form one mole of gaseous 1- ions

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15
Q

are second electron affinities exothermic or endothermic, and why?

A
  • second electron affinities are endothermic
  • a second electron is being gained by a negative ion, which repels the electron away
  • so energy must be put in to force the negatively charged electron onto the negative ion
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16
Q

what is the enthalpy change of hydration?

A

the enthalpy change when one mole of gaseous ions is dissolved in water to form one mole of aqueous ions, under standard conditions

17
Q

what are the properties of ionic compounds?

A
  • high melting and boiling points
  • soluble in polar solvents
  • conduct electricity when molten or in aqueous solution
18
Q

what are the two factors that affect lattice enthalpy?

A

ionic size and ionic charge

19
Q

how does ionic size affect lattice enthalpy?

A
  • ionic radius increases
  • attraction between ions decreases
  • lattice energy becomes less negative (less exothermic)
  • melting point decreases
20
Q

how does ionic charge affect lattice enthalpy?

A
  • ionic charge increases
  • attraction between ions increases
  • lattice enthalpy becomes more negative (more exothermic)
  • melting point increases
21
Q

what are the two factors affecting hydration enthalpy?

A

ionic size and ionic charge

22
Q

how does ionic size affect the hydration enthalpy?

A
  • ionic radius increases
  • attraction between ion and water molecules decreases
  • hydration energy becomes less negative
23
Q

how does ionic charge affect hydration enthalpy?

A
  • ionic charge increases
  • attraction with water molecules increases
  • hydration enthalpy becomes more negative
24
Q

what is entropy?

A

a measure of the dispersal of energy and disorder within the chemicals making up the chemical system

25
Q

how does entropy vary across the different states of matter?

A
  • solids have the smallest entropies
  • liquids have greater entropies
  • gases have the greatest entropies
26
Q

what factors control whether a reaction can occur?

A

a reaction can happen if the products have a lower overall energy than the reactants

27
Q

what is the free energy change?

A

the overall change in energy during a chemical reaction, denoted as ΔG

28
Q

what are the two types of energy that make up the free energy change?

A

the enthalpy change and the entropy change

29
Q

what is the condition for feasibility according to the Gibb’s equation?

A

for a reaction to be feasible, there must be a decrease in free energy: ΔG < 0

30
Q

what are the limitations of predictions made by ΔG about feasibility?

A
  • many reactions have a negative ΔG value but do not seem to take place
  • a large activation energy can result in a very slow rate of reaction
  • although the sign indicates thermodynamic feasibility, it takes no account of the kinetics or rate of a reaction
31
Q

what is reduction?

A

the gaining of electrons, decrease in oxidation number

32
Q

what is oxidation?

A

the loss of electrons, increase in oxidation number

33
Q

what is an oxidising agent?

A

takes electrons from the species being oxidised, contains the species being reduced

34
Q

what is a reducing agent?

A

adds electrons to the species being reduced, contains the species being oxidised

35
Q

what are the standard conditions?

A
  • a temperature of 298K
  • a pressure of 100kPa
  • concentration of 1.00 mol dm-3
36
Q

which electrode does oxidation and reduction occur at?

A

oxidation happens at the anode, reduction happens are the cathode

37
Q

which electrode is the positive terminal?

A

the cathode

38
Q

which electrode is the negative terminal?

A

the anode

39
Q

what is the function of the salt bridge?

A

in electrochemical cells, the salt bridge allows charge balance to be maintained in the cell

chemistry (9 decks)

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