Bh cycle and entropy test

enthalpy change

heat energy transferres in a reaction at constant pressure

enthalpy change symbol

ΔH

units of enthalpy change

kJ mol^-1

enthalpy change of atomisation of an element 

enthalpy change when 1 mole of gaseous atms is formed from an element under standard conditions

enthalpy change of atomisation symbol

enthalpy change of atomisation of cl

enthalpy change of atomisation of a compound

enthalpy change when 1 mole of a compound is converted to gaseous atoms under standard conditions

enthalpy change of atomisation of NaCl

second ionisation energy

energy needed to change 1 mole of gaseous 1+ ions atoms into 1 mole of gaseous 2+ ions

first electron affinity

energy needed to change 1 mole of gaseous atoms into 1 mole of gaseous 1- ions

second electron affinity

energy needed to change 1 mole of gaseous 1- into 1 mole of gaseous 2- ions

lattice enthalpy

enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions

lattice enthalpy symbol

lattice enthalpy of NaCl

enthalpy change of hydration

enthalpy change when 1 mole of gaseous ions is dissolved in water under standard conditions

enthalpy change of hydration symbol

enthalpy change of hydration of Na

enthalpy change of solution

enthalpy change when 1 mole of solute is dissolved in a solvent such as water under standard conditions

enthalpy change of solution symbol

enthalpy change of solution of NaCl

what is lattice enthalpy a measure of

ionic bond strength

Factors affecting lattice enthalpy

• ionic charge

  • ionic radius

how does ionic charge affect lattice enthalpy

• the higher the charge on the ions

• the stronger the electrostatic attraction between the ions

• so the more energy is released when an ionic lattice forms.

• more energy released meand lattice enthalpy will be more negative

• so lattice enthalpy for compounds with 2+ or 2- iions are more negative than 1+ or 1- ions

how does ionic radius affect lattice enthalpy

the smaller the ionic radii of the ions involved the higher the charge density of the ion this means the electrostatic attraction between the ions is greater so the lattice enthalpy is mor exothermic

born haber cycle example

what happens if there is 2 of a molecle in bohn haber cycle 

times enthalpy change of atomisation for element by 2 and either is ionisation energy or electron affinity by 2

what happens when a solid ionic lattice dissolves in water

• bonds between ions break to give gaseous ions which is endothermic,enthalpy change is opposite of lattice enthalpy

• bonds between ions and water and made-exothermic,enthalpy change of hydration

enthalpy change of solution equation

enthalpy of hydration-lattice enthalpy

enthalpy change of solution enthalpy cycle

factors affecting enthalpy of hydration

• ionic charge

  • ionic radius

how does ionic charge affect enthalpy of hydration

• ions with a greater charge have a greater enthalpy of hydration

• because ions with a higher charge are better at attracting water molecules than those with lower charges

• more energy is released when the bonds are made giving them a more exothermic enthalpy of hydration

how does ionic radius affect enthalpy of hydration

• smaller ions have greater enthalpy of hydration

• as smaller ions have a higher charge density than bigger ions

• they attract water molecules better and have more exothermic enthalpy of hydration

is lattice enthalpy endo or exothermic

exothermic

bond enthaly

The enthalpy change when 1 mole of a particular covalent bond in the gaseous state is broken.

why is the second and third electron affinities endothermic 

incoming electron is added to an already negative ion so energy is required to overcome the repulsive forces between the incoming electron and negative ion 

what is entropy

measure of dispersal of energy in a system

what does the greater the entropy mean

the more disordered the system

symbol for entropy

S

symbol for entropy change

ΔS

what happens to entropy as you go solid to liwuid to gas

becomes more disordered

what happens to entropy as you dissolve a solid

increases its entropy

what happens to entropy as there are more gaseous particles

increases

units of entropy change 

JK^-1mol^-1

when will chemical reactons only take place with entropy change

when overall entropy change is positive

entropy change of system equation

ΣSproducts - ΣSreactants

entropy change of surroundings equation 

-enthalpy change/temperature

what is units of enthalpy change in entropy change of surroundings equation 

Joules

what is units of temperature in entropy change of surroundings equation 

K

total entropy change 

entropy change of system + entropy change of surroundings

what happens to entropy as temperature increases

entropy increases

what is free energy change

measure used to predict whether a reaction is feasible

feasible reaction

reaction that once started will carry on to completion without any energy being supplied to it

when is a reaction feasbile 

if free energy change is negative or zero

gibbs / free energy change equation

units of free energy change

Jmol^-1

units of enthalpy change in gibbs equation 

Jmol^-1

why might a reaction not take place even if △G is negative

high activation energy,slow rate of reaction

equation to work out temperature at which reaction is feasible

△H/△S

id a reaction is exothermic and has a positive entropy change what  will △G always be 

negative

id a reaction is endothermic and has a negative entropy change what  will △G always be 

positive

if a reaction is exothermic and has negative entropy change when will it be feasible

low temperature

if a reaction is endothermic and has positive entropy change when will it be feasible

high ttemperatres

gibbs equation in y=mx + c form

△G=-△s T + △H

what is the gradient of straigt line gibbs

-△S

what is the y intercept of straight lien gibbs 

△H

enthaly change

is the heat energy transferred in a reaction at constant ressure ∆H

standard conditions for enthaly changes

100kPa

298K

ΔH°

standard states

hysical states of reactants under standard conditions

endthermic reaction

when energy is taken in from the surroundings so roducts have more energy than reactants heat taken in

endothermic enthaly change

ositive

exothermic reaction

when energy is released to surroundings roducts have less energy than reactants heat is given out

enthaly change of exothermic reaction

negative

overall enthaly change equation

energy needed to break bonds(reactants - energy released making bonds (roducts

activation energy

minimimum amiunt of energy for a chemical reaction to tak lave

activation energy on enthaly rofile diagrm

difference btween reactants and to of hum

exothermic enthaly rofile diagram

endothermic enthaly rofile diagram

standard enthaly change of reaction

• ∆r H

  • enthaly change when a reaction occurs in the molar quantities shown in the chemical equation under standard conditions with all reactants and roducts in their standard states

standard enthaly change of fromation

• ∆f H

  • enthaly change when 1 mole of a comound is formed from its elements in their standard states under standard conditions

standard enthaly change of combustion

• ∆c H

  • enthaly change when 1 mole of a substance is comletely burned in oxygen under standard conditions with all reactants and roducts in their standard syayes

standard enthaly change of neutralisation

• ∆neutH

• enthaly change when solutions of an acid and alkali react together to form 1 mole of water under standard conditions

calorimetry

exerimetnak method for finding enthaly change by measuring temerature chnage over time

how to measure enthlay changes in lab

• neutralisation,dislacement stick thermometer into solution in olysteren beaker

• combustion - copper calorimeter containing known mass of water burn and measure temerature change

equation for enthaly change

q=mc∆T

• q=energy change(j

• m=mass g

• c= secific heat caacity jg^1K^1

• ∆t temerature chnage K

secific heat caacity

energy required to raise 1g of subsatance by 1K without change of state

how to calculate nergy change er mole

qx10^-3/moles or kj/g x mr

errors with enthaly change exepriments

• calorimetry not comleteyly accurate

• heat loss can occurbut can insulate

• use secific heat cacity of water not solution

average bond enthaly

energy required to break one mole of the stated bond in a gaseoys state under standard conditions

hess law

total enthalychanges of reaction is alwys the ame no matter which route is taken

enthaloy change of formation hess law

arrows oint up

-Hf of reactanta + hf of roducts

enthaly change of cobustion hess law

oint down

H2O and CO2

reactants - products