thermochemistry Flashcards
1.exothermic reactions
2.endothermic reactions
- heat released, system cools down (-ve)
>most spontaneous reactions
{combustion}
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2.heat absorbed, temp high (+ve)
>non spontaneous are endo
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combustion of carbon enthalphy change value
-393.7 KJ/mol
haber process is an_____ process
exothermic
process which is;
1. always exo
2. always endo
- COMBUSTION
- IONISATION ENERGY
spontaneous and non spontaneous reactions
takes place without any outside assistance (e.g burning)
>its single directional
>irreversible
>mostly exothermic
[rusting of iron, burning of coal and hydrocarbon]
takes place with assistance
>reversible
>endothermic
[pumping water uhill, dissufion of gass from high to low]
*formation of nitric oxide N2 and O2 in air.
is heat and work a state function
NO.
state function is a thermodynamic state if macroscopic properties of P, V, T, n are known
is heat(q) a state property
NO.
heat: qty of energy that flows across the boundaryof a system due to a difference in temperature bw system and surrounding
>not a property
work
W=Fs.
workdone by the system= +ve
workdone on the system= -ve
1st law of thermodynamics equation
change in energy(E)=q+w
Enthalpy(H)
Sum of internal energy and product of pressure and volume.
H=E+PV
1.state fuction
2.measured in joules
St Enthalpy of reaction 🔺Hr
Amount of heat evolved/abdorbed at standard conditions states
Standard confitions
298K, 25⁰C
Enthalpy of formation
1 mol of a compound formed from its elements under standard states and conditions
May be exo or endo.
Enthalpy of atomisation
ENDO
1 mol of gaseous atoms formed from element under standard conditions
Enthalpy neutralisation
1 mol of H+ from an acid react with 1 mol OH- from a a base form one mol of water under st condition
Enthalpy combustion
EXO
1 mol substance completely burnt in Oxygen.
Enthalpy solution
EXO OR ENDO
1 mol of substance dissolved in solvent until no heat change
measurement of enthalpy of a reaction
glass calorimeter [reaction]
bomb calorimeter [combustion]
{measured at const volume}
heat capacity
q=c(sp heat)T
Born haber cycle
Energy change always 0
Used to calculate lattice energy of ionic compounds.
Lattice energy definition and dependant on?
Enthalpy of formation of 1mol of ionic compound from its gaseous ions.
Can be endo or exo
(Na+) + (Cl-)……..>NaCl. 🔺Hlatt= -787kjmol
Depends directly on +ve charge
E.g mg2+ has higher than Na+
Depends inversely on size
Lower size is higher lattice energy
NaCl enthalpy of formation value
-411
