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A HL Chemistry 2024/2025 > Reactivity 1.2 > Flashcards

Reactivity 1.2 Flashcards

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1
Q

Bond breaking… what energy?

A

Absorbs

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2
Q

Bond forming… what energy?

A

Releases

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3
Q

Energy is required to…

A

break a chemical bond (endothermic)

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4
Q

Energy is given out when..

A

chemical bonds are formed (exothermic)

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5
Q

Bond enthalpy values only refer to…

A

The gaseous state

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6
Q

Bond enthalpy units

A

kJmol-1

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7
Q

Bond breaking

A

Seperating atoms that are attracted by an electrostatic force

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8
Q

Bond making

A

Involves bringing together atoms that are attracted by an electrostatic force

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9
Q

DELETE

A

DELETE

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10
Q

Strength of bonds

A

Are influenced to some degree by the nature of other atoms attached to one or both of the bonding atoms

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11
Q

Average bond enthalpy

A

Average energy required to break one mole of the bond in similar compounds all in the gaseous state

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12
Q

Average bond enthalpy strength order

A

Single covalent < double covalent < triple covalent

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13
Q

When can you calculate enthalpy changes?

A

When all reactants and products are in the gaseous phase

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14
Q

Enthalpy change for a reaction is…

A

Total bonds enthalpies in reactants - total bond enthalpies in products

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15
Q

Why is calculated change in enthalpy different to that in the data booklet?

A

Values used are average values in similar compounds

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16
Q

Hess’s law of constant heat summation

A

The total energy change in a chemical reaction depends only upon the initial and final states and is independent of the reaction pathway

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17
Q

Energy cycle - what side is worth what?

A

Clockwise = anti clockwise

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18
Q

Standard enthalpy of atomisation

A

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

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19
Q

Enthalpy of formation

A

Enthalpy change when one more of product is formed from its elements in their standard state

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20
Q

Standard state rules (4)

A
  • HOFBrINCl are all diatomic, everything else in monotomic
  • Br2 and Hg are gases
  • Noble gases are all gases
  • Everything else is solid
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21
Q

First ionisation energy (IE)

A

Minimum energy required to remove one mole of electrons from one mole of gaseous atoms

22
Q

First affinity energy (EA)

A

Energy released when one mole of gaseous atoms gain an electron to form one mole of gaseous ions

23
Q

Lattice enthalpy (lat)

A

The energy needed to convert one mole of ionic solid into gaseous ions under standard conditions (ionic solid to gaseous ions)

24
Q

Enthalpy of atomisation (atm)

A

The enthalpy change that occurs when one mole of gaseous atoms is formed from the element in its standard state (standard state to a gas

25
Q

Enthalpy of sublimation (sub)

A

Enthalpy change when one mole of gaseous atoms is formed from the element in solid state

26
Q

Enthalpy of solution (sol)

A

The enthalpy change when 1 mole of solute is dissolved in solvent to infinite dilution at STP.

27
Q

Enthalpy of solution (sol) steps

A

1 - lattice enthalpy when lattice breaks into gaseous ions
2 - enthalpy of hydration, hydrates the gaseous ions to make them aqueous

28
Q

Enthalpy of hydration (hyd)

A

The enthalpy change when 1 mol of anhydrated substance is converted to 1 mol of hydrated substance

29
Q

Enthalpy of dissociation (dis)

A

Amount of energy required to break a chemical bond between two species

30
Q

How to calculate enthalpy of dissociation in diatomic molecules?

A

Use bond enthalpy from data booklet and half (Cl has half Cl2 enthalpy)

31
Q

Does the route taken affect the total enthalpy change?

A

No, Hess Law states it is independent (special case of law of conservation of energy)

32
Q

Why are the enthalpies of reactions only valid for reactions in the gaseous state?

A

It does not include intermolecular interactions

33
Q

What do energy cycles allow for?

A

The calculation of values corresponding to certain enthalpy changes which cannot be determined directly

34
Q

Average bond enthalpy

A

Energy required to break one mole of the same type of bonds in the gaseous state averaged over a variety of similar compounds

35
Q

Enthalpy of combustion (c)

A

The enthalpy change when one mole of substance in its standard state is completely combusted in oxygen under standard conditions

36
Q

Standard enthalpy of formation of an element in its normal standard state

A

Must be 0 (not for allotropes though)

37
Q

Hess’s Law of Constant Heat Summation

A

Total energy change in a chemical reaction depends only on the initial and final states and is independent of the reaction pathway

38
Q

Enthalpy of combustion cycle

A

H= Hc reactants - Hc product

39
Q

Enthalpy of formation cycle

A

H = Hf products - Hf reactants

40
Q

Ionisation enthalpy (IE) equations

A

M(g) -> M+(g) + e-
Always positive, endothermic

41
Q

Electron affinity (EA) equation

A

M (g) + e- = M- (g)
Always negative, exothermic

42
Q

Lattice enthalpy (latt) notes for equation

A

g + g -> s (Exothermic in formation)

s -> g + g (Endothermic in breakdown)

43
Q

Atomisation enthalpy (atm) equation and note

A

M (s) -> M (g)
Always positive H (endothermic)

44
Q

Covalent bond enthalpy equation and note

A

X (g) + Y (g) -> X-Y (s)
Exothermic (bond formation)

45
Q

What can a Born Haber cycle tell you?

A

The energy changes that occur when an ionic compound is formed

46
Q

What factors affect the size of the lattice enthalpy?

A

Ionic radius and charge of ion

47
Q

Ionic radius as a factor of lattice enthalpy

A

The smaller the ions, the closer they are together and the stronger the forces of attraction (larger lattice enthalpy)

48
Q

Ionic charge as a factor of lattice enthalpy

A

The greater charge, the stronger the forces of attraction, the greater the lattice enthalpy

49
Q

What are the lattice enthalpy values in a born haber cycle?

A

Experimental values as they are based on experimental data

50
Q

Born haber as a special case of Hess’s Law

A

It allows a lattice enthalpy to be calculated from other enthalpy changes

A HL Chemistry 2024/2025 (18 decks)

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