Thermodynamics - Born Haber Cycles Flashcards Preview

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Flashcards in Thermodynamics - Born Haber Cycles Deck (38):
1

What is the symbol for enthalpy change?

Delta H

2

What are standard conditions?

298K and 100kPa and all solutions at a concentration of 1moldm-3 and all substances present in their standard states

3

What is enthalpy change?

The heat energy change at constant pressure

4

Define enthalpy of lattice dissociation

The enthalpy change when one mole of an ionic compound is separated into its component gaseous ions

5

Is lattice dissociation endo or exothermic and why?

Endothermic because breaking bonds requires energy

6

Define enthalpy of lattice formation

The enthalpy when one mole of an ionic compound is formed from its constituent ions in the gaseous state

7

Is lattice formation exo or endothermic?

Exothermic bc making bonds releases energy

8

Define enthalpy of formation

The enthalpy change when one mole of a compound is formed from its elements when all the reactants and products are in their standard states under standard conditions

9

Define enthalpy of atomisation of an element

The enthalpy for the formation of one mole of gaseous atoms from the element in its standard state

10

Define bond dissociation enthalpy

The enthalpy change when one mole of a covalent bond is broken under standard conditions in the gaseous state

11

Is bond dissociation enthalpy endo or exothermic?

Endothermic

12

Define first ionisation enthalpy

The enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to produce one mole of gaseous ions with a single positive charge

13

Define second ionisation enthalpy

The enthalpy change when one mole of electrons is removed from one mole of gaseous ions with a single positive charge to form one mole of gaseous ions with a 2+ charge

14

Define third ionisation enthalpy

The enthalpy change when one mole of electrons is removed from one mole of gaseous ions with a 2+ charge to form one mole of gaseous ions with a 3+ charge

15

Define first electron affinity

The enthalpy change when one mole of gaseous atoms forms one mole of negative ions with a single negative charge

16

Define second electron affinity

The enthalpy change when one mole of gaseous ions with a single negative charge forms one mole of gaseous ions with a double negative charge

17

What two assumptions are made by the perfect ionic model?

Bonding in a compound is 100% ionic
The ions are perfect spheres and are not distorted

18

What does a difference in experimental lattice enthalpy and calculated lattice enthalpy show?

The compound has some covalent character

19

How do you calculate the enthalpy of solution?

Enthalpy of lattice dissociation + enthalpy of hydration

20

Define enthalpy of solution

The enthalpy change when one mole of solute dissolves in water

21

Define enthalpy of hydration

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

22

Are enthalpy of hydration values exo or endothermic and why?

Exothermic bc energy is released when ions are attracted to the polar water molecules

23

What does the value of the lattice enthalpy show?

A measure of the strength of the ionic bond

24

What does the strength of the ionic bond depend on?

Charge of the ion and their size

25

What is mean bond enthalpy?

The enthalpy needed to break one mole of a covalent bond averaged across many compounds containing that bond

26

Why is the bond enthalpy for diatomic molecules not averaged?

Because the bond only occurs in the diatomic molecules

27

Why are the values for second electron affinities positive?

Because there is repulsion between the negative ion and the negative electron being added

28

In a Born Haber cycle, what do arrows going up represent?

Endothermic processes

29

In a Born Haber cycle, what do arrows going down represent?

Exothermic processes

30

Why do smaller ions have a higher lattice enthalpy value?

Smaller so they pack more tightly together

31

Why do ions with a higher charge have a higher lattice enthalpy value?

Form stronger ionic bonds bc more attraction between the ions

32

Why is there a more negative enthalpy of hydration for smaller ions with the same charge?

Bc higher charge density so negative charge on the ion attracts the H+ on the water more strongly

33

What is the first law of Thermodynamics?

Energy cannot be created or destroyed

34

What is enthalpy?

The amount of chemical energy in a system at a constant pressure

35

What is the standard state of a substance?

Its pure, most stable form at 100kPa at a given temperature

36

What is the standard enthalpy change?

The enthalpy change under standard conditions of 298K and 100kPa with all reactants and products in their standard states

37

What is the standard enthalpy change of formation of an element?

0

38

What does Hess's Law state?

If a reaction can take place by more than one route, the overall enthalpy change is the same, regardless of the route, as long as the final and initial conditions are the same