1. Energy & Calorimetry
THERMOCHEMISTRY

2. What is “energy”? ENERGY is defined as “the ability to do work”
Work = force x distance
(work means moving something!)
Different forms of energy include:
electrical, solar, chemical, nuclear

3. Categories of Energy POTENTIAL energy of position or “stored” energy
KINETIC
energy of motion

4. HEAT ENERGY
Energy is absorbed or released as heat in chemical or physical changes – energy involved can be measured
DURING PHYSICAL/CHEMICAL CHANGES ENERGY AND MATTER ARE CONSERVED!
Heat energy impacts particle motion (atoms, ions, molecules) – more heat, more motion; less heat, less motion

5. Kinetic–Molecular Theory of Matter
Developed in late 19th century to account for behavior of atoms and molecules
Based on idea that particles of matter are always in motion – KINETIC ENERGY = ENERGY OF MOTION
Used to explain properties of solids, liquids & gases in terms of the energy of particles and forces that act between them

6. HEAT ENERGY
Temperature is a measure of the average kinetic energy of the particles in a sample of matter
Heat, represented by “q” for “Q”uanity of heat, is energy that transfers from one object to another because of a temperature difference between them
Heat flows from an object of higher temperature to one with a lower temperature

7. HEAT ENERGY Heat flow is measured in two common units:
the calorie and the joule
Food is usually measured in Calories:
1 Calorie = 1 kilocalorie = 1000 calories
A JOULE is the SI unit of heat as well as all other forms of energy and is abbreviated J
4.184 J = 1 calories

8. MEASURING HEAT GAINED/LOST
Q = m t cp
Q = quantity of heat
m = mass in grams
t = change in temperature
Cp = specific heat of the substance

9. SPECIFIC HEAT
A physical property of matter that describes how well a substance can absorb or release heat
It is a measure of how many joules of energy the substance absorbs or loses per gram for each degree change in temperature
Specific heat unit: J/g-C

10. Specific Heat
The amount of heat required to raise the temperature of one gram of substance by one degree Celsius.
Ex Cp water = J/g-C

11. Specific Heat Calculation
Cp = Q__
m x t
Temperature Change Calculation
t = Q___
cp x m

12. A Bomb Calorimeter

13. A Cheaper Calorimeter

14. Table of Specific Heats

15. Calculations involving Specific Heat
Q = m x T x cp
m = mass in grams
Q = Heat lost or gained
T = Temperature change
cp = Specific Heat

16. Sample problem
How much heat is absorbed when 250 g of water is heated from 27 C to 85 C?
Q = m x t x cp
Q = (250 g) ( 58 C) (4.184 J/g-C) =
60668 J

17. Temperature Temperature Scales Name Melting Temp Boiling Temp
ice water
C Celsius C C
K Kelvin K K
F Fahrenheit 32 F F

18. PHASE CHANGE
Involves PHYSICAL CHANGES from solid to liquid, liquid to solid, liquid to gas, etc
Particles absorb or release heat during phase changes
NOTE: THE TEMPERATURE OF THE MATTER
DOES NOT CHANGE DURING A
PHASE CHANGE!

20. PHASE CHANGE
The heat absorbed or released during a phase change changes the position of the particles to one another
DURING A PHASE CHANGE, THERE IS A CHANGE IN THE POSITION OF THE PARTICLES TO ONE ANOTHER AND THUS A CHANGE IN POTENTIAL ENERGY
During a temperature change the heat absorbed or released affects the AVERAGE KINETIC ENERGY OF THE MOLECULES

21. HEAT AND MATTER KINETIC ENERGY – energy of motion
KINETIC ENERGY CHANGES WITH
TEMPERATURE CHANGES
POTENTIAL ENERGY – energy of position
POTENTIAL ENERGY CHANGES
DURING PHASE CHANGES

23. Common Phase Changes condensation deposition vaporization sublimation
Fusion/melting
Freezing/crystallization

24. Phase Differences Solid – definite volume and shape; particles packed
in fixed positions.
Liquid – definite volume but indefinite shape;
particles close together but not in fixed
positions
Gas – neither definite volume nor definite shape;
particles are at great distances from one
another

25. Three Phases

26. CALCULATIONS INVOLVING HEAT INFORMATION:
CP ice = 2.06 J/gC
Cp water = J/g C
Cp steam = 2.02 J/gC
Heat of fusion for ice= 334 J/g
(Heat of crystallization)
Heat of vaporization of water = 2260 J/g
(Heat of condensation)

27. Temperature Change Q = m t Cp ice = m t (2.06 J/g-C)
Q = m t Cp water = m t (4.184 J/g-C)
Q = m t Cp steam = m t (2.02 J/g-C)

28. Phase Change (Remember, no T change during Phase Change)
Q = m x heat of fusion = m x 334 J/g
(heat added to melt each gram of ice)
Q = m x heat of vaporization =m x 2260 J/g
(heat added to boil each gram of water)