1. Enthalpy
1105

2. What are we going to do today?
NaOH + H2O  -OH + Na+
HCl + H2O  H3O + + Cl-
HCl + NaOH → H2O + Na+ Cl- + Heat
Today we will look at the products
Measure quantity of heat transferred in a system.
And to measure heat we use: Q

3. Enthalpy You can only measure the change in enthalpy State Function
Energy Change Per Mole
Think of it like the energy in the bonds
State Function
Depends only on the current state of the system (comp., vol., temp., etc)
Independent of the path only initial and final
Energy content of a system
The increase in enthalpy of a system is equal to the added heat
So…… ∆H = Q =Heat of Reaction

4. Enthalpy ∆H = HP – HR From the Graph Would ∆H be “-” or “+”? ∆H = “-”
Exothermic (HR > HP)
Heat is produced ∆H H HR HP
R → P (Progress)

5. Enthalpy
Endothermic
∆H = “+”
Hp > Hr
Heat is absorbed

6. Important Thermodynamics
Gibbs free energy (SUPER IMPORTANT TO KNOW)
∆G= ∆H - T ∆S
Enthalpy = H Heat Transferred
Entropy = S measure of disorder
Temperature = T
Gibbs free Energy = E exchange
State Function
Property of a system dependent only on its current state
Depends only on the initial and final state

7. Experiment Our Goal: Determine heat of reactions
Must Determine Heat Product To Give The ∆H
Q = Amount Of Heat Transferred In A Reaction
MicroLab R P
Universe
Surrounding
System
Stirrer

8. Objective of the exp.
Solvation NaOH solid in water = Do not throw away this solution you will needed for exp.3
Neutralization HCl (aq) and NaOH (aq) equal concentration
Reaction NaOH (solid ) + in HCl (aq)
So… In theory ≈ 3

9. Experiment QSurr. = - QSys. Will measure the amount of heat transfer
Remember Qsurroundings?
Q= S.H. * m * ∆T
Since the density of water is one
QSurr. = S.H. * (d * V) * ∆T
QSurr. = - QSys.
In order for surrounding to gain energy, system had to lose energy

10. Calculations 1 calorie = 4.184 joules Molarity NaOH = mol / L
So…Molarity * volume in L = mol
∆H = QSys. in KJ / mols NaOH
Exothermic is –
endothermic is+
Don not throw your first solution you are going to need it for exp. 3 mL
1.00 g
Total mL
change T OC J
g O