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Chemistry A2 > F325 - Energy > Flashcards

F325 - Energy Flashcards

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0
Q

What is the enthalpy change of solution?

A

The energy released when one mole of an ionic solid dissolves in sufficient water to form a solution of infinite dilution.

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1
Q

What is lattice enthalpy?

A

Enthalpy change when one mole of an ionic compound is formed from it’s gaseous ions.

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2
Q

What is the enthalpy of hydration?

A

The energy released when one mole of gaseous ions dissolves in sufficient water to form a solution of infinite dilution.

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3
Q

What is the enthalpy change of atomisation?

A

Enthalpy change when one mole of gaseous atoms are formed from the element in its standard state.

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4
Q

What is the first electron affinity?

A

Enthalpy change when one electron is added to each of one mole of gaseous atoms to form one mole of gaseous 1- ions.

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5
Q

What is the second electron affinity?

A

Enthalpy change when one electron is added to each of one mole of gaseous 1- ions to form one mole of gaseous 2- ions.

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6
Q

What is the first ionisation energy?

A

Energy needed to remove one electron from each atom in one mole of gaseous atoms of an element.

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7
Q

What is meant by the term successive ionisation energies?

A

Energies needed to remove each successive electron from each atom in one mole of gaseous positively charged ions.

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8
Q

What is the enthalpy of formation?

A

Enthalpy change when one mole of a compound is made from its constituent elements.

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9
Q

What properties affect the magnitude of lattice enthalpy?

A

Size of ions (ionic radius) and charge on ions (charge density).

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10
Q

What happens to the lattice enthalpy as the size of the ion increases?

A

Becomes less exothermic (less negative)

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11
Q

What happens to the lattice enthalpy as the charge on the ion increases?

A

Becomes more exothermic (more negative)

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12
Q

What is entropy?

A

The degree of disorder of a system.

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13
Q

Which state if matter would have the lowest entropy?

A

Solids (as their particles are arranged in near rows and are ordered)

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14
Q

Which state of matter would have he highest entropy?

A

Gases (as the interactions between molecules are negligible)

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15
Q

What happens to the magnitude of entropy when a solid dissolves? Why?

A

Increases as the lattice dissolves (breaks down) to be in solution.

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16
Q

What happens to the magnitude of entropy for a reaction where a larger number of moles of gas are produced?

A

Increases (more disordered)

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17
Q

What happens to the magnitude of entropy for a reaction where a larger number of moles of gas are reacted?

A

Decreases (less disordered)

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18
Q

How is the entropy change for a reaction calculated?

A

Change in entropy = entropy of products - entropy of reactants

19
Q

What does the tendency for a reaction to take place depend on?

A
  • T, temperature
  • S, entropy change in the system
  • H, enthalpy change with the surroundings
20
Q

What is meant by the term free energy change of a reaction?

A

The maximum useful work that can be done by a chemical reaction.

21
Q

What is the Gibbs free energy equation?

A

{delta}G = {delta}H - T{delta}S

22
Q

What is needed for a reaction to be spontaneous?

A

Free energy is negative (more than 20kJ/mol)

23
Q

How can an endothermic reaction occur spontaneously?

A
  • enthalpy value is small
  • entropy is positive (increase in disorder)
  • temperature is high enough so that the overall energy is negative
24
Q

What is meant by the term redox?

A

When reduction and oxidation take place simultaneously.

25
Q

What is meant by the term oxidation number?

A

A number assigned to the atoms of each element in an ion or compound determined from the number of electrons gained or lost.

26
Q

What is a half-equation?

A

An equation that describes what is happening in one half-cell. Or an equation which describes only the reduction or only the oxidation reaction.

27
Q

What is an oxidising agent?

A

A species that takes one or more electrons away from another species in a reaction?

28
Q

What is a reducing agent?

A

A species that donates one or more electrons to another species in a reaction.

29
Q

What is added to balance the oxidation numbers in a half-equation?

A

Electrons

30
Q

What is added to balance charge in a half-equation?

A

Hydrogen ions

31
Q

What is added to balance hydrogen and oxygen in a half-equation?

A

Water

32
Q

What needs to be balanced when constructing an overall redox equation?

A

Electrons

33
Q

What is the standard electrode potential?

A

The electrode potential of a half-cell when measured with a standard hydrogen electrode as the other half-cell. All conditions must be standard.

34
Q

What is taking place in the half-cell if the standard electrode potential is negative?

A

The half-cell donates electrons to the standard hydrogen electrode. Greater tendency to proceed in the reverse direction.

35
Q

What takes place in a half-cell when the standard electrode potential is positive?

A

The half-cell receives electrons from the standard hydrogen electrode. Greater tendency to proceed in forward direction.

36
Q

What is used as the electrode in a half-cell when measuring the electrode potential is ions of the same element in different oxidation states?

A

Platinum

37
Q

What are the standard conditions required for measuring the standard electrode potentials?

A
  • 1 atm of pressure/100 kPa/ 1 bar
  • 298 K
  • 1 mol/dm^3 solutions
38
Q

What are the limitations associated with predicting whether or not a reaction will occur using standard electrode potentials?

A
  • actual conditions are not likely to be standard
  • if concentration is not standard then it can be measured against the SHE
  • if concentration is greater on LHS E will be more positive
  • if concentration is greater on RHS E will be less positive
  • does not predict rate of reaction which might be too slow
39
Q

What is a difference between a storage cell and a fuel cell?

A

Fuel cells use energy from the reaction of a fuel with oxygen and storage cells use redox reactions.

40
Q

Where do the electrons flow in a cell?

A

External circuit

41
Q

Where do the ions flow in a cell?

A

Across the salt bridge/membrane

42
Q

What is the only byproduct in a hydrogen-oxygen fuel cell?

A

Water

43
Q

What do the anode and cathode do with electrons respectively in a fuel cell?

A

Anode - supplies

Cathode - receives

44
Q

What are the limitations of hydrogen-oxygen fuel cells?

A
  • limited lifetime
  • expensive to produce (electrodes and membrane)
  • production of toxic products in manufacturing
  • storage of hydrogen
  • refuelling
  • engineering fuel cell vehicles
  • transport of hydrogen to filling stations
  • people adapting to change
45
Q

How can the storage of hydrogen problem be overcome?

A
  • store hydrogen as a liquid (still costly and expensive)
  • adsorb onto a surface (eg nanotubes)
  • absorb by metal alloys
46
Q

What are the advantages of hydrogen-oxygen fuel cells?

A
  • less pollution and carbon dioxide
  • greater efficiency
  • hydrogen economy is better (obtained from electrolysis of water)

Chemistry A2 (6 decks)

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