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Chemistry OCR A A level > Enthalpy and Entropy > Flashcards

Enthalpy and Entropy Flashcards

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1
Q

What is lattice enthalpy?

A

A measure of strength of ionic bonding in a giant ionic lattice

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2
Q

Define lattice enthalpy of formation

A

Enthalpy change that occurs during formation of one mole of an ionic compound from its gaseous ions under standard conditions

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3
Q

Is lattice enthalpy endothermic or exothermic?

A

Exothermic

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4
Q

Define standard enthalpy change of formation

A

Enthalpy change that occurs when one mole of a compound is formed from its elements under standard conditions with all reactants and products in standard states

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5
Q

Define standard enthalpy change of atomisation

A

One mole of gaseous atoms formed from elements in standard states under standard conditions

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6
Q

Is standard enthalpy change of atomisation endothermic or exothermic?

A

Endothermic

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7
Q

What is the enthalpy change of atomisation equal to when an element is a gas in a standard state?

A

Enthalpy of atomisation is related to bond enthalpy of bond being broken. So the value is equal to the bond enthalpy

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8
Q

Define first ionisation energy

A

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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9
Q

Is first ionisation energy endothermic or exothermic? Why?

A

Endothermic, energy required to overcome attraction between electron and nucleus

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10
Q

What is electron affinity and is it endothermic or exothermic?

A

Energy to gain electrons, exothermic

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11
Q

Define standard enthalpy change of solution

A

Energy change that takes place when one mole of a solute dissolves in a solvent

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12
Q

Define standard enthalpy change of hydration

A

Enthalpy change that accompanies dissolving gaseous ion water to form one mole of gaseous ions

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13
Q

What are the two processes that take place when a solid dissolves?

A

Ionic lattice breaks up

Water molecules are attracted to and surround ions

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14
Q

Give 3 key properties of ionic compounds

A

High melting and boiling points
Soluble in polar solvents
Conduct electricity when molten or in aqueous solution

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15
Q

Describe the effect of increased ionic size on lattice enthalpy

A

Ionic radius increases
Attraction between ions decreases
Lattice energy is less negative
Melting point decreases

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16
Q

Describe the effect of increased ionic charge on lattice enthalpy

A

Ionic charge increases
Attraction between ions increases
Lattice energy becomes more negative
Melting point increases

17
Q

How do you estimate melting points?

A

Lattice enthalpy may need to consider other factors such as packing of ions in an ionic lattice

18
Q

Describe the effect of increased ionic size on enthalpy of hydration

A

Ionic radius increases
Attraction decreases between ion and water molecules
Hydration energy is less negative

19
Q

Describe the effect of increased ionic charge on enthalpy of hydration

A

Ionic charge increases
Attraction with water molecules increases
Hydration energy becomes more negative

20
Q

At what point does a substance dissolve?

A

When the sum of the hydration enthalpies is greater than magnitude of lattice enthalpy then overall enthalpy change is exothermic and it dissolves

21
Q

Define entropy

A

The dispersal of energy within the chemical making up a chemical system

22
Q

What is the general rule regarding entropy with solids, liquids and gases?

A

Solids have the smallest entropies

Gases have the greatest entropies

23
Q

How does an increase in the number of gaseous molecules affect entropy?

A

Increases entropy as there is more disorder

24
Q

Define standard entropy

A

The entropy of one molecule of a substance under standard conditions

25
Q

How do you calculate the entropy of a reaction?

A

Entropy of products- entropy of reactants

26
Q

Define feasibility

A

Whether a reaction could happen and is energetically feasible

27
Q

Define free energy change

A

Overall change in energy during a chemical reaction

28
Q

Give Gibbs’ equation

A

Free energy change = enthalpy change - entropy change at temperature of reaction

29
Q

What is the condition of feasibility?

A

Free energy change < 0

30
Q

When is feasibility supported?

A

Enthalpy change is negative

Entropy change is positive

31
Q

What is the major limitation of prediction of feasibility?

A

Activation Energy

Chemistry OCR A A level (20 decks)

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