THERMODYNAMICS

Question 1

define enthalpy change of formation

Answer 1

when 1 mole of compound is formed from its elements under standard conditions and all reactants and products being in standard states

Question 2

why is enthalpy change of formation always 0

Answer 2

by definition

Question 3

define first ionisation energy

Answer 3

enthalpy change required to remove 1 mole of electron from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a +1 charge

Question 4

define in enthalpy of atomisation

Answer 4

enthalpy changes when 1 mole of gaseous atom is formed from the elements in standard state

Question 5

define bond enthalpy

Answer 5

energy required to break a particular covalent bond in one mole of molecules in gaseous state

Question 6

define in electron affinity

Answer 6

enthalpy change that occurs when 1 mole of gaseous atoms gain electrons to form 1 mol of gaseous ions- always exothermic

Question 7

what is the trend of sizes of ions

Answer 7

larger the ions the less negative the enthalpies of lattice formation, as ions increase the charge increase and becomes further apart so have a weaker attraction between them so electrostatic forces between oppositely charged ions in the lattice will be weaker

Question 8

what is the trend in charge of ions

Answer 8

the bigger the charge the greater the attraction between ions so they have a stronger lattice enthalpy, this is because they have strong electrostatic charge between oppositely charged ions in a lattice

Question 9

define the perfect ionic model

Answer 9

theoretical lattice enthalpies will assume a perfect ionic model where the ion are 100% ionic and spherical and results in attraction being purely electrostatic

Question 10

what is the real experimental value in born haber

Answer 10

if a compound shows covalent character the theoretical and born hater lattice enthalpy will differ, so more covalent character the bigger difference between both values

Question 11

trend in enthalpy value across a period

Answer 11

they become less ionic and more covalent leading to discrepancy

Question 12

define enthalpies of solution

Answer 12

standard enthalpy change when 1 mol of an ionic solid dissolves in a large enough amount of water to ensure the dissolves ions are separated and do not interact with each other

Question 13

define enthalpies of hydration

Answer 13

enthalpy change when 1 mol of gaseous ions become aqueous ions this gives out energy because bonds are made between the ions the water molecules.

Question 14

what happens when an ionic solid is dissolved in water

Answer 14

positive and negative ions will form, the water is polar so forms ion-dipole attraction with ion present in the solution.Oxygen is attracted to positive and hydrogen is attracted to negative

Question 15

how to calculate enthalpy of hydration

Answer 15

enthalpy of hydration = enthalpy of lattice formation - enthalpy of solution

Question 16

what is a spontaneous process

Answer 16

will proceed on its own without having any external influence

Question 17

what is feasability

Answer 17

describes how energetically favourable the reaction is

Question 18

how to calculate standard entropy change

Answer 18

sum of products - sum of reactant

Question 19

define entropy

Answer 19

how disordered the system, the possible arrangements of particles and their energy in a given system

Question 20

what does an increase in entropy mean

Answer 20

system will be more energetically stable and becomes more disordered

Question 21

what happens to feasibility during exothermic

Answer 21

enthalpy change is negative, if the system is positive then the Gibbs is negative and therefore is feasible so regardless of the temperature an exothermic reaction with a positive system is feasible

Question 22

what happens to feasibility during endothermic

Answer 22

enthalpy change is positive, if the system is negative this means Gibbs will be positive so reaction will not be feasible so regardless of the temperature it will be endothermic with a negative system and can’t ever be feasible.

Question 23

what’s happens to feasibility during positive enthalpy change and system is positive

Answer 23

Gibbs will be feasible and at low temperature the reaction will not be feasible, at higher temperature the reaction will be more feasible. certain reactions that are not feasible at room temperature can be feasible at higher temperature