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chem yr 13 NI > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

Hess’s law

A

Enthalpy change for a chemical reaction is the same regardless of route taken

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2
Q

Standard enthalpy of formation

A

Enthalpy change when one mole of a compound is formed from its elements under standard conditions
All reactants and products in their standard states

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3
Q

Standard Enthalpy of combustion

A

Enthalpy change when one mole of a compound is completely burned in oxygen under standard conditions
All reactants and products in their standard states

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4
Q

Standard Enthalpy of atomisation

A

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

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5
Q

First ionisation energy

A

Enthalpy change when one mole of electron is removed from one mole of atoms in the gaseous state

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6
Q

First electron affinity

A

Standard Enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions

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7
Q

Lattice formation Enthalpy

A

Enthalpy change when one mole of solid ionic compound is formed from gaseous ions

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8
Q

Lattice dissociation Enthalpy

A

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

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9
Q

Standard Enthalpy of hydration

A

Enthalpy change when one molecule of gaseous ions is converted into one mole of aqueous ions

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10
Q

Standard Enthalpy of solution

A

Enthalpy change when one mole of solute dissolves in enough solvent to form a solution in which the ions are far enough apart to not interact with each other

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11
Q

Important born-hater cycle rules

A

Enthalpy change is positive - arrow points upwards
Enthalpy change is negative - arrow points downwards
State symbols in every stage of the cycle

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12
Q

Order of born haber cycle

A

Start with elements in their standard states
Atomise the metal
Atomise the non metal
Ionise the metal
Electron affinity for the non metal
Lattice formation of the whole compound

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13
Q

What are the 2 factors that determine how exothermic a lattice Enthalpy will be

A

Charge on the ions
Size of the ions

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14
Q

Charge on the ions

A

Higher charge on ion the stronger the ionic bond
Greater lattice Enthalpy
More energy given out in the formation of lattice
More energy needed to break apart the ionic lattice

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15
Q

Size of the ions

A

Smaller the ion the stronger the attraction so stronger the ionic binding
So greater the lattice Enthalpy

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16
Q

More negative lattice formation so

A

Stronger ionic bonds
In answers use CRAM
charge of the ions,radius of the ions,attraction between ions and more exothermic/endothermic

17
Q

Actual and theoretical value

A

If both values are close then indicates that the compound shows almost purely ionic bonding
If actual value is higher than theoretical value it’s because compound has some covalent character

18
Q

What is covalent character

A

+ve ion is quite small which quite a strong +ve charge
-ve ion is large with a diffuse electron cloud
+ve ion is strongly polarising
The electron cloud about the -ve ion becomes distorted
Some of the electron density is shared

19
Q

Perfect ionic model

A

Purely ionic bonding with no covalent character
Ions act as point charges
Ions act as perfect spheres which cannot be distorted

20
Q

Stages of Enthalpy of solution

A

1-lattice dissociation
2-hydration

21
Q

Enthalpy of solution calculation

A

> H Sol = >H LD + >H Hyd

22
Q

Why do chemical reactions take place

A

Reaction has to be feasible and spontaneous

23
Q

What determines if a reaction is feasible

A

Temperature
Enthalpy - most feasible reactions are exothermic
Entropy

24
Q

Entropy meaning

A

Entropy is a measure of disorder
Units are jk-1mol-1
Is disorder increases entropy is positive
Is disorder decreases entropy is negative
Entropy increases with change of state s-l-g
If mols of products are higher than mol of reactants increases entropy

25
Q

Calculating entropy change

A

Entropy change = (sum of entropy of products) - (sum of entropy of reactants)

26
Q

Gibbs free entropy change

A

Gibbs = Enthalpy change - temp x entropy change

27
Q

Gibbs and graphs

A

Y= Gibbs
X = t
M =- entropy change
Y intercept = Enthalpy change

chem yr 13 NI (17 decks)

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