1. Thermochemistry

2. Energy Transformations
“Thermochemistry” - concerned with heat changes that occur during chemical reactions
Energy - capacity for doing work or supplying heat
if within the chemical substances- called chemical potential energy

3. Energy Transformations
Gasoline contains a significant amount of chemical potential energy
Heat - represented by “q”, is energy that transfers from one object to another, because of a temperature difference between them.
flows from warmer  cooler object

4. Exothermic and Endothermic Processes
Essentially all chemical reactions and changes in physical state involve either:
release of heat, or
absorption of heat

5. Exothermic and Endothermic Processes
The Law of Conservation of Energy: energy is neither created nor destroyed. (a closed system…no matter can escape)
All the energy is accounted for as work, stored energy, or heat.

6. In an open system, a system may exchange matter and heat with the surroundings (like a system of boiling liquid losing matter and heat with the vapor).

7. Exothermic and Endothermic Processes
Heat flowing into a system from it’s surroundings:
defined as positive
q has a positive value
called endothermic
system gains heat (gets warmer) as the surroundings cool down

8. Exothermic and Endothermic Processes
Heat flowing out of a system into it’s surroundings:
defined as negative
q has a negative value
called exothermic
system loses heat (gets cooler) as the surroundings heat up

9. Exothermic and Endothermic
Every reaction has an energy change associated with it
Energy is stored in bonds between atoms

10. Heat Capacity and Specific Heat
Specific Heat Capacity (abbreviated “C”) - the amount of heat it takes to raise the temperature of 1 gram of the substance by 1oC
often called simply “Specific Heat”
Water has a HUGE value, when it is compared to other chemicals

11. Heat Capacity and Specific Heat
For water:
it takes a long time to heat up, and
it takes a long time to cool off!
Water is used as a coolant!

12. Heat Capacity and Specific Heat
To calculate, use the formula: q = mass (in grams) x T x C
On ref. table
heat is abbreviated as “q”
T = change in temperature
C = Specific Heat
Units are either: J/(g oC) or cal/(g oC)

13. Calorimetry
Calorimetry - the measurement of the heat into or out of a system for chemical and physical processes.
Based on the fact that the heat released = the heat absorbed
The device used to measure the absorption or release of heat in chemical or physical processes is called a “Calorimeter”

14. Calorimetry
Foam cups are excellent heat insulators, and are commonly used as simple calorimeters under constant pressure.
For systems at constant pressure, the “heat content” is the same as a property called Enthalpy (H) of the system
(They are good because they are well-insulated.)

15. Calorimetry Changes in enthalpy = H q = H
Thus, q = H = m x C x T (on ref. table)
H is negative for an exothermic reaction
H is positive for an endothermic reaction

16. Calorimetry
Calorimetry experiments can be performed at a constant volume using a device called a “bomb calorimeter” - a closed system
Used by nutritionists to measure energy content of food

17. Exothermic
The products are lower in energy than the reactants
Thus, energy is released.
ΔH = -395 kJ
The negative sign does not mean negative energy, but instead that energy is lost.

18. C + O2 → CO2 + 395 kJ Energy Reactants Products ® C + O2
395kJ given off
CO2

19. Endothermic
The products are higher in energy than the reactants
Thus, energy is absorbed.
ΔH = +176 kJ
The positive sign means energy is absorbed

20. CaCO3 → CaO + CO2 CaCO3 + 176 kJ → CaO + CO2 Energy Reactants Products
CaO + CO2
176 kJ absorbed
CaCO3

21. Heat in Changes of State
1. Heat of Fusion (Hf) = the heat absorbed by one mole of a substance in melting from a solid to a liquid
q = mass x Hf (no temperature change)

22. 2. Heat of Vaporization (Hv) = the amount of heat necessary to vaporize one mole of a given liquid.
q = mass x Hv (no temperature change)

23. Heating Curve for Water
120 °C steam
100 °C water  steam
50°C liquid water
0 °C ice liquid
-10 °C ice
Heat added 

28. Heating or Cooling Curve
A heating or cooling curve is a simple line graph that shows the phase changes a given substance undergoes with increasing or decreasing temperature.

29. Phase Diagram
The triple point of the substance represents the only point in the phase diagram in which all three states are in equilibrium. 
The critical point of the substance, is the highest temperature and pressure at which a gas and a liquid can coexist at equilibrium.
The phase diagram shows, in pressure-temperature space, the lines of equilibrium or phase boundaries between the three phases of solid, liquid, and gas.