Summary AQA A level chemistry energetics full revision notes

EnerqetICS
4. ENDOTHERMIC AND EXOTHERMI, 4.2 ENTHALPY, 4.3 MEASURING

are
ploce, chemcol bonds breale and new ones
When a chemical reaction reacion lakcs
formed. Bond breakings uses Cnerqy making bonds eleases eneryy

combustion, neutralis otion
Exothem - ene as qiven out. eg Lhermal decomposticn
Endothemc energy takenn in the ceverse
exothermicn one direction, t w be endotherm(
a ceactionIs

fuels, which hawe very exothemic
lhemochemistry enables us to compare effiueny f kJmoL.
ceactions when combusted. Enthalpy s measured n


Enthalpy changes
Enthalp chanqe - heat changc at constoat pcessurepressure, 248| temperature
100LPa
Standa conditONS for woeasuing AH-

Ln an exotheCmc reaction, AH 1s negatue
endo thecmi reaction, DH s posutave
af substances affect eathalpy
State sybais are impatast - state
ENTHALPy
ENTHALPY

R - AH

REACTION PROGRESS
REACTON PROGRESS

level diagram for an
Enthalpy level diaaram for
Eathalpy
endother mic reactian
exothernic reactian

mole of a substance is formed trom ts
when one
DH - enthalpy chane with adreactants cnd prsdcts
standard conditions
(onstituent elenents under
n ther standard states
a substane is conpletely burned
mole of
enthalpy cnange when one reactants and products their
with all
urygen under stondard conditions,
standad states