1. Thermochemistry (The study of energy transfers) Mr. Forte Atascadero High School

2. Units of Energy  The most common energy unit is the joule (J).  1000 J = 1 kilojoule (kJ)  The calorie (cal) is also used.  1.000 cal = 4.184 J  The nutritional Calorie is actually 1000 cal or one kilocalorie (kcal)

3. Kinetic vs. Potential Energy  The energy of a phase change is potential energy, energy of position.  During a phase change there is no change in the average kinetic energy (temperature) of the particles.  In general, the energy change from solid- liquid phase is much less than liquid-gas phase.

4. Heat vs. Temperature  Temperature is the measure of the average kinetic energy of particles (related to particle motion).  Heat is energy that transfers between substances at different temperatures (hotter to colder).  A cup of water has less heat energy to transfer than a bucket of water at the same temperature.

5. Temperature Change (  T)  To calculate the amount of heat energy lost or gained during a change in temperature, the specific heat formula is used: Q = m · s ·  T  Where Q = heat energy; m = mass; and s = the object’s specific heat capacity.  Specific Heat Capacity (s) is the quantity of energy needed to change one gram of the substance by 1.0  C.

6. Common Specific Heat Capacities See pg.297 ( J / g ·  C)  Water (l) 4.184  Water (s) 2.03  Aluminum (s) 0.89  Iron (s) 0.45  Copper (s) 0.38  Silver (s)0.24  Gold (s) 0.13

7. Calorimetry  Calorimetry is the study of heat flow and measurement during physical and chemical changes.  A coffee cup calorimeter is often used in high school chemistry labs to conduct calorimetry experiments.

8. Coffee cup Calorimeter Thermometer Stirrer Coffee cup

9. Practice Problem  How much heat energy is needed to raise the temperature of 5.0 grams of liquid water by 12 degrees Celsius? (specific heat of water is 4.184 J/g ·  C) Solution: Q = (5.0 g) · (4.184 J/g ·  C) · (12  C) = 251 J

10. Phase Changes and Energy  The quantity of energy needed to change one mole of a solid to liquid is called its molar heat of fusion. Energy is absorbed (endothermic). Reversing the process releases this same quantity of energy (exothermic).  The quantity of energy needed to change one mole of a liquid to gas is called its molar heat of vaporization. This is also an endothermic process.

11. Change of Phase  To calculate the amount of heat energy lost or gained during a change in phase, the heat of fusion or vaporization formula is used: Q = mol ·  H fus or Q = mol ·  H vap  Where Q = heat energy; mol = moles; and  H represents the latent heat of fusion or vaporization of the substance per mole.

12. Change of Phase  Heats of Fusion or vaporization can also be given as per gram quantities. The equations then become: Q = m ·  H fus or Q = m ·  H vap  Where Q = heat energy; m = mass; and  H represents the latent heat of fusion or vaporization of the substance on a per gram basis.