Can enthalpy be measure directly?
No
Enthalpy change symbol
🔼H
Delta H
Enthaply change definition
The enthalpy change of a reaction is the heat energy change with its surroundings at constant pressure.
Enthalpy change units
kj mol^(-1)
Delta meaning
Change
Standard enthalpy changes are measured at…?
Standard pressure (100 kPa) Standard temperature (298 K)
Symbol ΔHθ. But θ is superscript
-ΔΗ is it exothermic or endothermic?
Exothermic
+ΔΗ is it exothermic or endothermic?
Endothermic
GRAPHS
SEE PAPER
Standard enthalpy of reaction symbol
θ
ΔΗ
R
The r for reaction is replaced by a specific letter for particular standard enthalpies
Standard enthalpy of Formation symbol
θ
ΔΗ
f
Standard enthalpy of formation definition
This is the enthalpy change when 1 MOLE of a substance is FORMED from its ELEMENTS under standard conditions (100kPa and 298k) with all substances in their standard STATES (eg. Solid, liquid gas)
Standard enthalpy of formation value of an element in its standard state
Must be 0
Standard enthalpy of formation equation for H2O
H2 + 1/2 O2 ➡️ H2O
To form one mole of water
Standard enthalpy of combustion symbol
θ
ΔΗ
c
Standard enthalpy of combustion definition
This is the enthalpy change when 1 MOLE of a substance undergoes COMPLETE COMBUSTION under standard conditions (100kPa and 298K) with all substances being in their standard states
What is meant by the term ‘standard states’ of a substance
Normal state at room temperature eg. Solid, liquid or gas
What are standard conditions
100kPa (kilo pascals)
298K (kelvin)
Standard enthalpy of combustion equation for CH4
CH4 + 2O2 ➡️ CO2 + 2H2O
Standard enthalpy of atomization symbol
θ
ΔΗ
a
Standard enthalpy of atomization definition
This is the enthaply change when 1 MOLE of GASEOUS ATOMS of a substance are FORMED from the substance in its standard state under standard conditions (100kPa and 298K)
Standard enthalpy of atomization equation for chlorine
1/2 Cl2 (g) ➡️ Cl (g)
Cl2 is how is appears normally then Cl is the one mole that is formed
Standard enthalpy of neutralization symbol
θ
ΔΗ
n
Standard Enthalpy of neutralization definition
This is the Standard Enthalpy change when 1 MOLE of WATER is produced by the reaction of an ACID and a BASE under standard conditions (100kPa and 298K) with all substances being in their standard states
Standard Enthalpy of neutralization equation for sulphuric acid and sodium hydroxide
BALANCED EQUATION. H2SO4 + 2NaOH ➡️ Na2SO4 + 2H2O
(Wrong as 2 moles of water)
Answer: 1/2 H2SO4 + NaOH ➡️ 1/2 Na2SO4 + H2O
In an exotherimic reaction does it give out energy to its surroundings or take energy in? And does the temperature of the reaction decrease or increase?
Gives OUT energy to surroundings
Reaction temperature gies UP
so -ΔΗ as the products of the reaction end up with LESS energy than the reactants
In an endothermic reaction does it give out energy to its surroundings or take energy in? And does the temperature of the reaction decrease or increase?
Takes IN energy from surroundings
Reaction temperature DEACREASES
Products have MORE energy than the reactants so ΔΗ is a positive value as
Give the notation for an enthaply change under standard conditions at a temperature of 298K
θ
ΔΗ
298
Describe the difference between endothermic and exothermic reactions
Exothermic gives OUT heat
Endothermic takes IN heat
Enthalpy definition
The enthalphy of a system is a measure of the energy stored in (or heat content) of a system. Symbol H