1. Part I An introduction to Thermochemistry
Thermodynamics
Part I
An introduction to
Thermochemistry

2. Thermochemistry The study of the energy evolved or absorbed
in chemical reactions and any physical
transformations, such as melting and boiling.
Generally is concerned with energy exchange accompanying transformations, such as mixing, phase transitions & chemical reactions
Includes calculations of such quantities as
the heat capacity, heats of combustion, heats
of formation, heats of fusion, enthalpy,
and Gibbs Free Energy.

3. Thermochemistry H-H bond C-C bond C-H bond 436 kJ/mole 332 kJ/mole
Energy (heat) is involved in all chemical reactions
Energy is stored in chemical bonds
Energy is released or absorbed when bonds break or form in a chemical reaction
H-H bond
436 kJ/mole
C-C bond
332 kJ/mole
C-H bond
418 kJ/mole

4. Enthalpy (∆ H) ∆ H = Enthalpy
is equal to the change in the internal energy of the system, plus the work that the system has done on its surroundings
change in enthalpy is the heat/energy absorbed or produced by a chemical reaction.
∆ H = Enthalpy
(heat of a reaction)
Endothermic vs. Exothermic Reactions

5. Endothermic Reactionsin
“thermic”
heat
energy is absorbed (put into) a chemical reaction
energy/heat is a reactant
∆ H has a positive value (+ ∆ H)
Reactants + energy → Products
Reactants ∆ H → Products +
Reactants → Products ∆ H = ##

6. ex:
CO H2O kJ/mole → CH O2

7. analysis of reactants, products & energy
Stored energy
Stability
less
more
more stable
less stable
Energy must be put into reactants to cause the chemical reaction
∆ H = kJ/mole

8. - Exothermic Reactions Reactants → Products + energy
out
“thermic”
heat
energy is released in a chemical reaction
energy/heat is on the products side
∆ H has a negative value (- ∆ H)
Reactants → Products + energy
Reactants → Products ∆ H -
Reactants → Products ∆ H = ##

9. ex:
2 Ag + 2 HCN → 2 AgCN + H kJ/mole

10. analysis of reactants, products & energy
Stored energy
Stability
more
less
less stable
more stable
unstable reactants release their energy
∆ H = kJ/mole

11. Bomb Calorimeter device used to measure the heat of chemical reaction
Exothermic reaction heats up water
Temp of water decreases in Endothermic Reaction
Specific Heat Capacity of Water = J/gC

12. Specific Heat Capacity
the measure of heat or thermal energy required to increase the temperature of a unit quantity of a substance by one unit.
Energy needed to raise 1 gram of a substance 1 degree Celsius
Water = J/gC
Aluminum = J/gC
Methane = 2.20 J/gC
Tungsten = J/gC

13. Calculating Enthalpy Changes Experimentally
using a calorimetry
∆ H = m x ∆ T x Cp
mass x temp change x specific heat

14. ∆ H = 63,094.72 J ∆ H = m x ∆ T x Cp ∆ H = - 63.09 kJ x x
problem #1
Calculate the heat of reaction if 412 grams of NaOH heats 520 grams of water from 22 C to 51 C
∆ H = m x ∆ T x Cp x x
520 g
29 C
4.184 J/gC
∆ H = 63, J
∆ H = kJ

15. ∆ H = 110,546.28 J ∆ H = m x ∆ T x Cp ∆ H = + 110.55 kJ x x
problem #2
A 1,560 gram cube of Aluminum has an initial temperature of 98 C and is cooled to 19 C. Determine the enthaply change.
∆ H = m x ∆ T x Cp x x
1,560 g
79 C
0.897 J/gC
∆ H = 110, J
∆ H = kJ