thermodynamics

Question 1

define empalthy change of formation?

Answer 1

The empalthy change for one mole of a molecule to be formed from its constituent elements in its standard state under standard conditions

Question 2

define lattice empalthy change of formation

Answer 2

the empalthy for one mole of solid ionic compound to be formed from gaseous ions under standard conditions

Question 3

define lattice empalthy change of dissociation

Answer 3

the empalthy for one mole of an ionic solid to dissociate to its gaseous ions under standard conditions

Question 4

define empalthy change of dissociation

Answer 4

the empalthy for one mole of bonds of the same type of molecule in the gaseous state is broken

Question 5

define empalthy change of 1st ionisation

Answer 5

the empalthy for one mole of gaseuous atoms to form one mole of 1+ gaseous ions by removing an electron

Question 6

define empalthy change of 2nd ionisation

Answer 6

the empalthy for one mole atom to form 1 mole 2+ gaseous atom to be formed from 1+ gaseous atom be removing an electron

Question 7

define empalthy of atomisation?f

Answer 7

the empalthy of one mole of gaseous atom is made from an element in its standard form

Question 8

define empalthy change of 1st electron affinity?

Answer 8

empalthy for one mole of gaseous atom to form one mole 1- gaseous ion by gaining an electron

Question 9

define empalthy change of 2nd electron affinity?

Answer 9

the empalthy for one mole of 1- gaseous ion to form one mole 2- gaseous ion by addinng an electron

Question 10

in born haber cycles how does the arrow direction affect empalthy change?

Answer 10

moving up is endothermic (positive empalthy change)

moving down is exothermic (negative empalthy change)

Question 11

what is a pure ionic compound?

Answer 11

ions that are perfectly spherical

the charge is evenly distributed in the sphere

Question 12

what does it mean if you conduct an experiment and the lattice empalthy is different to the theoretical value

Answer 12

The compound does not follow the perfect ionic model and has some covalent chracteristic. This is because the positive ion distorts the charge distribuition in the negative ion by polarising it

Question 13

what does the greater the positive charge of the ion result in ,in terms of pure ionic bond?

Answer 13

the greater the positive charge of the ion the highr change of their being more covalent bonds and a less pure ionic bond

Question 14

what does the greater the positive charge of the ion result in ,in terms of pure ionic bond?

Answer 14

the greater the positive charge of the ion the highr change of their being more covalent bonds and a less pure ionic bond

Question 15

what is the empalthy of solution?

Answer 15

the empalthy for one mole of an ionic substance to be dissolved by the minimum amount of solvent to ensure no further enthalpy change is observed upon further dilution

Question 16

what is the empalthy of hydration?

Answer 16

when 1 mole of aqueous ions are made from 1 mole of gaseous ions

Question 17

what is the empalthy of solution equal to

Answer 17

empalthy of solution = empalthy of hydration +empalthy dissociation

Question 18

what is the hydration empalthy based off?

Answer 18

the large the ion charge the larger the empalthy
the smaller the ion (the higher up it is on the periodic table) the larger the empalthy
meaning it can have a stronger attraction to water

Question 19

what is required for a substance to be dissolved?

Answer 19

substance bonds must break(endothermic - requires energy)

new bonds must be formed between solvent and substance which are greater or same strength (exothermic)

Question 20

describe an ionic lattice getting dissolved?

Answer 20

ionic lattice in solid form
subtance bond broken to create free moving ions
bonds formed between ion and water water
the water is hydrated
most ionic substances are dissolved by polar substances where the delta positive H attracts the negative ion and the delta negative O attracts the positive ion

Question 21

what is entropy?

Answer 21

Entropy is the number of ways energy can be shared out between particles.
the more disorder the more higher the level of entropy

Question 22

how does particle arrangment and amount affect particle.

Answer 22

Gases have the highest entropy as they have the most space to move around in.
The more particles their are the higher the entropy so molecules with more moles have higher entropy

Question 23

if a reaction is enthalpically unfavourable how can it still undergo?

Answer 23

If a reaction is endothermic it can still spontaenously react if changes in entropy overcome it

Question 24

what is entropy measured in?

Answer 24

JK/MOL

Question 25

how is entropy calculated?

Answer 25

products- reactants

Question 26

what is a favourable entropy?

Answer 26

A positive entropy is favouirable

Question 27

what is a favoured enthalpy

Answer 27

a negative enthalpy is favourable as it is exothermic

Question 28

what is gibbs free energy

Answer 28

tells us whether a reaction is feasible

Question 29

what is the equation for gibbs free energy/

Answer 29

gibbs free energy= enthalpy change - (entropy change x temp) | J/mol J/mol J/K/mol K

Question 30

what does gibbs free energy have to be for a reaction to be feasible?

Answer 30

G has to be 0 or less

Question 31

If a reaction is feasible why could it still not happen??

Answer 31

activation energy too high | Rate of reaction too low

Question 32

A 5.00 g sample of potassium chloride was added to 50.0 g of water initially at 20.0 °C. The mixture was stirred and as the potassium chloride dissolved, the temperature of the solution decreased. Describe the steps you would take to determine an accurate minimum temperature that is not influenced by heat from the surroundings.

Answer 32

start a clock when KCL is added to water record the temp every minute for 5 minutes plot a graph vs time extrapolate back to time of mixing=0 at determine temperature

Question 33

Suggest why hydration of the chloride ion is an exothermic process?

Answer 33

H2O is polar and has H delta postive | the cl- attracts the H in water molecules

Question 34

what is meant by perfect ionic model?

Answer 34

No covalent character | Only ionic bonding

Question 35

Suggest why a value for the enthalpy of solution of magnesium oxide is not found in any data books.

Answer 35

MgO reacts with water to form MgOH so it is not soluble

Question 36

State the meaning of the symbol ϴ in ∆Hϴ .

Answer 36

standard pressure

Question 37

The freezing of water is an exothermic process. Give one reason why the temperature of a sample of water can stay at a constant value of 0 °C when it freezes.

Answer 37

the heat given out escapes

Question 38

Pure ice can look pale blue when illuminated by white light. Suggest an explanation for this observation.

Answer 38

White light is absorded by light | blue light is reflected back

Question 39

In terms of the forces acting on particles, suggest one reason why the first electron affinity of oxygen is an exothermic process

Answer 39

Their is a strong attraction between the nucleus of the O and the electron

Question 40

State whether you would expect the value of the theoretical enthalpy of lattice dissociation for silver chloride to be greater than, equal to or less than that for silver bromide. Explain your answer.

Answer 40

``` greater chloride ions (CL- ) smaller than BR- so stronger attraction with Ag+ ```

Question 41

Using a Born–Haber cycle, a value of –905 kJ mol–1 was determined for the lattice enthalpy of silver chloride. A value for the lattice enthalpy of silver chloride using the ionic model was –833 kJ mol–1 . Explain what a scientist would be able to deduce from a comparison of these values.

Answer 41

Ions are not arranged in perfect spheres their is slight covalent character hence the model has a lower value