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Chemistry > Enthalpy And Entropy > Flashcards

Enthalpy And Entropy Flashcards

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1
Q

Lattice Enthalpy

A

Measure of strength of ionic bonding in a giant ionic lattice
Involves bond formation this always Exothermic -ve

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2
Q

Born haber cycles

A

Calculate lattice formation indirectly using known energy changes

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3
Q

Elements in standard states to ionic lattice

A

Formation of gaseous atoms endo
Formation of gaseous ions endo
Lattice enthalpy gas -> solid lattice exo

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4
Q

Standard Enthalpy change of formation

A

Enthalpy change that takes place when one mole of compound is formed from its elements under standard conditions

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5
Q

Standard Enthalpy change of atomisation

A

Enthalpy change that takes place for the formation of 1 mol of gaseous atoms from the element units standard state
Always endothermic bonds breaking

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6
Q

First ionisation energy

A

Energy required to remove one electron from each atom in 1 mil of gaseous atoms
Endothermic

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7
Q

First electron affinity

A

The Enthalpy change that takes place when one electron is added to each atom in 1 mol of gaseous atoms
Exothermic

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8
Q

Lattice Enthalpy equation

A

= Enthalpy of formation - (atomisation + ionisation energies + electron affinities)

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9
Q

Second electron affinity

A

Addition of 1 electron to every ion in 1 mol of ions in gas form
Endothermic - energy required to overcome repel of -ve ion

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10
Q

Standard Enthalpy change of solution

A

Enthalpy change that takes place when 1 mol of a solute dissolves in a solvent
The partial - oxygen attracted to +ve ion
The partial + hydrogen attracted to the -ve ion

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11
Q

What mass is used in q=mc T

A

Mass of solution not he mass of water

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12
Q

Dissolving process

A

Ionic lattice breaks up
Desperate gaseous ions interact w polar water molecules to form aq ions

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13
Q

Enthalpy change of hydration

A

Enthalpy change that accompanies dissolving of gaseous ion in water to form 1 mil of aq ions
Exothermic

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14
Q

Factors affecting lattice Enthalpy

A

Ionic size
Ionic charge

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15
Q

Ionic size effect le

A

Ionic radius increase attraction decreases
lattice energy less negative
Melting point decreases
Make Enthalpy of sol less Exothermic down group

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16
Q

Ionic charge effect le

A

Ionic charge increase
Attraction increases
Lattice Enthalpy more exothermic
Melting point increases

17
Q

Factors effecting hydration

A

Ionic size - radius increase hydration energy less negative ( less attraction water an ions) make enthalpy of sol less exothermic
Ionic charge- increases attraction increases hydration becomes more negative

18
Q

Predicting solubility

A

If the sum of hydration enthalpies is greater than the magnitude of lattice Enthalpy overall Enthalpy change will be exothermic
Compound should dissolve
However this also depends on temp and entropy

19
Q

Entropy

A

How energy is dispersed and becoming spread out
The greater the Enthalpy the greater the dispersal of energy and the greater the disorder
J/K per mol

20
Q

Entropy of states

A

Solids smallest
Liquids greater
Gases greatest

21
Q

Above 0K

A

Energy becomes dispersed amongst particles and all substances have a positive entropy

22
Q

Predicting entropy changes

A

If a system becomes more random energy can be spread out more - there will be a positive entropy change
If system becomes less random entropy change will be negative

23
Q

Changes of state

A

From solid to liquid to gas entropy increases as energy is spread out more

24
Q

Reaction produce gas entropy

A

Entropy increases as the disorder of particles increases energy is more spread out
If No of moles of gas decrease there’s a decrease in randomness energy is spread out less entropy is negative

25
Q

Standard entropy

A

Entropy of 1 mil of a substance under standard conditions
Always positive endothermic

26
Q

Entropy change

A

Products - reactants

27
Q

Free energy change

A

The overall change in energy during a chemical reaction
Made up of Enthalpy change and entropy

28
Q

Gibbs equation

A

Enthalpy - temperature (K) x entropy

29
Q

Feasibility of reaction

A

For a reaction to happen the free energy change needs to be less than 0

30
Q

Why can some endothermic reactions take place at room temp

A

Need to calculate entropy and free energy
The free energy change will be less than 0
Entropy and Enthalpy need to be low

31
Q

Limitations of feasibility predictions

A

It takes no account of kinetics or rate of reaction some reactions are vvvvv slow

Chemistry (20 decks)

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