How a Salt Forms

Question 1

Define Hess’s Law

Answer 1

If a reaction can take place by more one route, the enthalpy change for the reaction is the same for both routes

Question 2

Define standard enthalpy of combustion

Answer 2

when 1 mol of a substance is burnt completely in n excess of oxygen under standard conditions

Question 3

Define standard enthalpy of neutralisation

Answer 3

when an acid and alkali react to form 1 mol of water under standard conditions

Question 4

Define standard enthalpy change of reaction

Answer 4

when equation quantities of materials react under standard conditions in standard states

Question 5

Define standard enthalpy of formation

Answer 5

when 1 mol of a substance is formed from its elements in their natural states under standard conditions

Question 6

What are the standard conditions

Answer 6

298K

101kPa

Question 7

What does a the cycle look like when you’re given standard enthalpy changes of combustion and a reaction

Answer 7

Reaction given goes along top
Co2 and H2O at the bottom in correct molar quantities from the reactants
Arrows point down from reactants and the products to the CO2 and H2O

Question 8

What does the cycle look like when you’re given standard enthalpies of formation, and you want to work out the enthalpy change for the combustion of something

Answer 8

Equation given along top
Elements in natural states along the bottom,make sure only 1 mol of product can be formed from them
Arrows pointing up from elements to products and reactants of top equation, ignore oxygen

Question 9

what is lattice enthalpy

Answer 9

energy released when 1 mole of a crystal is formed from its constituent ions in their gaseous state

Question 10

what sign will lattice enthalpy have and why

Answer 10

negative

bonds are forming releasing energy

Question 11

why cant you measure lattice enthalpy directly

Answer 11

cant get gaseous ions separately from the ions of the opposite charge

Question 12

what is enthalpy of atomisation

Answer 12

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

Question 13

what is ionisation energy

Answer 13

energy required to remove 1 mole of electrons from 1 mole of gaseous atoms

Question 14

what is electron affinity

Answer 14

enthalpy change accompanying the gain of 1 mol of electrons by 1 mol of atoms in the gaseous phase

Question 15

why is the 2nd electron affinity vale for O +

Answer 15

O- ion and electrons are both negative

meaning energy is required to overcome repulsion

Question 16

what is enthalpy of formation

Answer 16

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

Question 17

is the lattice enthalpy always positive or negative

Answer 17

negative

Question 18

what happens to the arrows in a born haber cycle when O- needs another electron added

Answer 18

Requires lots of energy (endothermic), so arrows go down and then back up

Question 19

what is enthalpy of solution

Answer 19

enthalpy change that occurs when 1 mole of an ionic solid dissolves in water

Question 20

what is the enthalpy of hydration of an ion

Answer 20

the enthalpy that occurs when 1 mole of a gaseous ion is completely hydrated by water

Question 21

conditions needed for the hydration of an ion

Answer 21

25oC

101kPa

Question 22

turning an ionic solid into gaseous ions is known as?

Answer 22

lattice dissociation enthalpy

Question 23

what does a higher charge density mean

Answer 23

better at attracting water, so more energy released= more exothermic

Question 24

what does having smaller ions mean

Answer 24

higher charge density, so better at attracting water, so more energy released= more exothermic

Question 25

what happens as lattice enthalpy increases

Answer 25

more exothermic, so the ionic lattice becomes more stable

Question 26

what is entropy

Answer 26

a measure of the number of ways that particles can be arranged and the number of ways the energy can be shared out between particles

particles like disorder= more energetically stable

Question 27

what happens to reactions if disorder increases

Answer 27

they tend to happen spontaneously

Question 28

what symbol is used to name the amount of energy available due to the arrangement of particles

Answer 28

entropy with the symbol (S)

Question 29

values of enthalpy and entropy being released

Answer 29

enthalpy- ∆H-ve

entropy- S+ve

Question 30

enthalpy and entropy units

Answer 30

enthalpy- Kj/mol

entropy- jK-1mol-1

Question 31

how to calculate ∆Stotal

Answer 31

= ∆Ssystem + ∆Ssurroundings

Question 32

how to calculate ∆Ssystem

Answer 32

= ∑(entropy of products) - ∑(entropy of reactants)

Question 33

how to calculate ∆Ssurroundings

Answer 33

= - ∆H/T

enthalpy in j/mol
temp in K

Question 34

how to calculate ∆Htotal

Answer 34

=∆Hproducts - ∆Hreactants

Question 35

what is free energy

Answer 35

combines enthalpy and entropy to work out if a reaction is feasible or spontaneous at room temp

Question 36

symbol for (Gibbs) free energy

Answer 36

G

Question 37

how to work out ∆G

Answer 37

= ∆H - T∆Ssytem

temp in K
∆S must be in kJ
∆H in kJ
∆G is in kJmol-1

Question 38

when is a reaction feasible using ∆G

Answer 38

when its negative (energy is given out)

Question 39

what happens when ∆G = 0

Answer 39

reaction at equilibrium
∆G= ∆H- T∆S
∆H= T∆S

Question 40

When is a reaction spontaneous

Answer 40

when delta h is more negative than delta s