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Chemistry > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

What is the standard enthalpy 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 being in their standard states

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2
Q

What is the first ionisation enthalpy?

A

Standard enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to give one mole of gaseous ions, each with a single positive charge

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3
Q

What is the standard enthalpy of atomisation?

A

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

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4
Q

What is mean bond enthalpy?

A

Enthalpy change when one mole of gaseous molecules each break a covalent bond to form two free radicals averaged over a range of compounds

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5
Q

What is the first electron affinity?

A

Standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a single negative charge, under standard conditions

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6
Q

What is lattice formation enthalpy?

A

Standard enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions

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7
Q

What is lattice dissociation?

A

Standard enthalpy change when one mole of solid ionic compound dissociated into its gaseous ions

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8
Q

What is the standard enthalpy of hydration?

A

The standard enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions

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9
Q

What is the standard enthalpy of solution?

A

The standard enthalpy change when one mole of solute dissolves to form its aqueous ions

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10
Q

What two key factors determine how exothermic a lattice enthalpy is?

A

Charge on the ions
Size of the ion (ionic radius)

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11
Q

How to increase the lattice enthalpy of a compound? (2)

A

The greater the charge on the ion, the greater its attraction to an oppositely charged ion
The smaller the ion the greater the attraction to an oppositely charged ion

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12
Q

What does a more negative lattice enthalpy of formation show about the ionic bonds?
What does a more positive lattice enthalpy of dissociation show? (1)

A

Stronger ionic bonds

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13
Q

What is covalent character in ionic bonding? (1)

A

Some of the electron density is shared

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14
Q

What characteristics must a compound have to show covalent character? (2)

A

A positive ion which is small and highly charge (i.e. is very polarising)
A negative ion which is large and highly charged (i.e. is very polarisable)

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15
Q

What is the perfect ionic model?

A

Compounds which display purely ionic bonding with no covalent character and ions are point charges

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16
Q

Explain the meaning of the term ‘perfect ionic model’ (2)

A

Ions have point charges
Only electrostatic attractions between oppositely charged ions

17
Q

What is the Born Haber experimental model (2)

A

Takes into account covalent character and ions are polarisable

18
Q

If an ionic compound has no covalent character what does this mean about the lattice enthalpy of formation (1)

A

Lattice enthalpy of formation calculated by perfect ionic model is equal to the lattice enthalpy of formation calculated by experimental model

19
Q

If an ionic compound has covalent character what does this mean about the lattice enthalpy of formation and why (2)

A

Lattice enthalpy of formation calculated by perfect ionic model is less exothermic than the lattice enthalpy of formation calculated by experimental model
Experimental Born Haber allows for covalent character and predicts stronger bonding

20
Q

What 3 factors determine if energy is feasible? (3)

A

Temperature
Enthalpy
Entropy

21
Q

What is entropy (1)

A

A measure of the amount of ‘disorder’ in a system

22
Q

How to calculate entropy change (1)

A

sum of entropy of product - sum of entropy of reactants

23
Q

What equation demonstrates the relationship between temperature, enthalpy and entropy? (1)

A

Gibbs Free Energy = enthalpy change - (temperature x entropy change)

24
Q

When is a reaction feasible? (1)

A

When Gibbs free energy is equal to or less than zero

25
Q

How can you rearrange the Gibbs free equation to make temperature the subject of the formula? (1)

A

temperature = enthalpy change / entropy change

26
Q

What happens to Gibbs free energy when the enthalpy change is negative and entropy change is positive and what happens if temperature is increased? (2)

A

Gibbs free energy is always negative at any temperature
If temperature is increased Gibbs free energy becomes more negative as T∆S gets bigger

27
Q

What happens to Gibbs free energy when the enthalpy change is positive and entropy change is negative and what happens if temperature is increased? (2)

A

Gibbs free energy is always positive at any temperature
If temperature is increased Gibbs free energy becomes more positive as T∆S gets bigger

28
Q

What happens to Gibbs free energy when the enthalpy change is negative and entropy change is negative and what happens if temperature is increased? (3)

A

∆G is becoming more positive because T∆S gets bigger
∆G will be negative when ∆H>T∆S
Gibbs free energy is negative at low temperatures

29
Q

What happens to Gibbs free energy when the enthalpy change is positive and entropy change is positive and what happens if temperature is increased?

A

∆G is becoming more negative because T∆S gets bigger
∆G will be negative when ∆H<T∆S
If temperature is increased Gibbs free energy becomes more negative

30
Q

What is second ionisation energy?

A

Enthalpy change when one mole of electrons is removed from one mole of gaseous +1 ions to form one mole of gaseous +2 ions

31
Q

What is second electron affinity?

A

Enthalpy change when one mole of gaseous 1- ions gains one mole of electrons to form one mole of gaseous 2- ions

32
Q

Compare the general entropy values for solids, liquids and gases

A

solids < liquids < gases

33
Q

What are the limitations of using G as an indicator of whether a reaction will occur (2)

A

Gibbs free energy only indicates if a reaction is feasible
It does not take into account the rate of reaction

34
Q

Why is entropy zero at 0 kelvin (2)

A

No disorder - molecules have no kinetic energy so are not moving/vibrating and cannot be arranged in any other way

35
Q

How is it possible for the temperature of a substance undergoing an endothermic reaction to stay constant (1)

A

The heat that is given out escapes to the surroundings

Chemistry (28 decks)

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