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A-level AQA Chemistry - Physical > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

What is the symbol for enthalpy change?

What is the definition of enthalpy change?

What are the standard conditions for an enthalpy change that was measured under standard conditions?

A

Delta H

The heat energy transferred in a reaction at constant pressure

298 K and 100 kPa.

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2
Q

Describe exothermic reactions

A

Have a negative delta H value because heat energy is given out

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3
Q

Describe endothermic reactions

A

Have a positive delta H value because heat energy is absorbed

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4
Q

Enthalpy change of formation

A

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions

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5
Q

Bond dissociation enthalpy

A

The enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken

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6
Q

Enthalpy change of atomisation of an element

A

The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state

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7
Q

Enthalpy change of atomisation of a compound

A

The enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms

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8
Q

First ionisation energy

A

The enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous ions

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9
Q

Second ionisation energy

A

The enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions

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10
Q

First electron affinity

A

The enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms

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11
Q

Second electron affinity

A

The enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions

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12
Q

Enthalpy change of hydration

A

The enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions

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13
Q

Enthalpy change of solution

A

The enthalpy change when 1 mole of solute is dissolved in enough solvent that no further enthalpy change occurs on further dilution

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14
Q

Lattice enthalpy of formation

Is it an exothermic or endothermic reaction?

A

The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions

Exothermic

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15
Q

Lattice enthalpy of dissociation

Is it an exothermic or endothermic reaction?

A

The enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions under standard conditions

Endothermic

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16
Q

What is lattice enthalpy a measure of?

A

Ionic bond strength

17
Q

Two definitions of entropy

A

The number of ways that particles can be arranged

The number of ways that the energy can be shared out between the particles

18
Q

The more disordered the particles are…

What does a large positive value of entropy show?

A

The higher the entropy is

A high level of disorder

19
Q

In entropy, more particles means…

Why is this?

A

More entropy

Entropy increases because the number of moles increases

20
Q

Feasible reaction

A

Reactions that happen by themselves without the addition of energy

21
Q

What is the symbol for entropy change?

What is the equation for calculating entropy change?

A

Delta S

Entropy change= Entropy of products - Entropy of reactants

22
Q

Standard entropy of a substance (with numbers)

A

The entropy of 1 mole of that substance under standard conditions (pressure of 100 kPa and temperature of 298 K)

23
Q

Symbol for free energy change

Definition for free energy change

Equation for calculating free energy change

Give units

A

Delta G

A measure used to predict whether a reaction is feasible

Delta G= Delta H - ( T x Delta S)

Delta G= J mol -1
Delta H= J mol -1
T= K
Delta S= J K -1 mol -1

24
Q

If Delta G is negative or equal to zero…

A

The reaction might happen by itself (ie feasible)

25
Q

Describe reactions that are feasible at any temperature

A

If a reaction is exothermic (negative delta H) and has a positive entropy change, then delta G is always negative since Delta G= Delta H - ( T x Delta S)

26
Q

Describe reactions that are not feasible at any temperature

A

If a reaction is endothermic (positive delta H) and has a negative entropy change, then delta G is always positive

27
Q

What happens in a reaction if delta H is positive (endothermic) and delta S is positive?

A

The reaction won’t be feasible at some temperatures but will be at a high enough temperature

28
Q

What happens in a reaction if delta H is negative (exothermic) and delta S is negative?

A

The reaction will be feasible at lower temperatures but won’t be feasible at higher temperatures

29
Q

When is a reaction just feasible?

Equation for calculating temperature at which a reaction becomes feasible

A

When delta G is zero

T= Delta H -:- Delta S

T= enthalpy change -:- entropy change

A-level AQA Chemistry - Physical (10 decks)

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