1. Thermodynamics

2. Energy Ability to do work Units– Joules (J), we will use “kJ”
Can be converted to different types
Energy change results from forming and breaking chemical bonds in reactions

3. Basic Energy Types Kinetic Energy– energy of “motion”
Potential Energy– “stored” energy

4. System vs. Surroundings

5. Types of Systems
Open System
Closed System
Isolated System

7. Heat (q) Energy transfer between a system and the surroundings
Transfer is instant from high----low temperature until equilibrium
Temperature—
Measure of heat, “hot/cold”
the average kinetic energy of molecules

8. Heat (q) continued Kinetic theory of heat Increase in heat results in
Heat increase resulting in temperature change causes an increase in the average motion of particles within the system.
Increase in heat results in
Energy transfer
Increase in both potential and kinetic energies

9. Thermodynamics 101 First Law of Thermodynamics
Energy is conserved in a reaction (it cannot be created or destroyed)---sound familiar???
Math representation: ΔEtotal = ΔEsys + ΔEsurr = 0
Δ= “change in”
ΔΕ= positive (+), energy gained by system
ΔΕ= negative (-), energy lost by system
Total energy = sum of the energy of each part in a chemical reaction

10. Basic Terminology Heat = transfer of energy
Temperature = measurement of heat
System = the area or space we focus on
Surroundings = everything else apart from the system
Boundary = separates system and surroundings

11. Calorimetry
How do we find the change in energy/heat transfer that occurs in chemical reactions???

12. Calorimetry
Experimentally “measuring” heat transfer for a chemical reaction or chemical compound
Calorimeter
Instrument used to determine the heat transfer of a chemical reaction
Determines how much energy is in food
Observing temperature change within water around a reaction container
** assume a closed system, isolated container
No matter, no heat/energy lost
Constant volume

14. Specific Heat
Amount of heat required to increase the temperature of 1g of a chemical substance by 1°C
Units: cal/g-K or J/g-K
4.184 J = 1 cal, K = °C
Allows us to calculate how much heat is released or absorbed by a substance ! ! !
Unique to each chemical substance
Al(s) = 0.901J/g°K
H2O(l) = 4.18 J/g°K

15. Specific Heat Equations
q = smΔΤ
s/Cp = specific heat (values found in reference table)
m = mass in grams
ΔΤ= change in temperature

16. Example 1: How much energy is required to warm 420 g of water in a water bottle from 25C to 37C ?
C(H2O (l)) = 4.18 J/g• C
ΔT = = 12 C
Q = mc ΔT
Q = (420 g)(4.18 J/g•  C)(12 C)
Q = J or 21 kJ

17. Example 2: How much energy is released by cooling 755 g of iron from 132 C to 12 C ?
Q = ?
m = 755 g
cFe = 0.45 J/g•C
ΔT= 132 C - 12 C = 120 C
Q = mc ΔT
Q = (755g)(0.45 J/g•C)(120 C)
Q = 40,700 J

18. “Coffee Cup” calorimeter
Styrofoam cup with known water mass in calorimeter
Assume no heat loss on walls
Initial water temp and then chemical placed inside
Final temperature recorded
Any temperature increase has to be from the heat lost by the substance SOOO
All the heat lost from the chemical reaction or substance is transferred to H2O in calorimeter

20. “Coffee Cup” calorimeter (cont.)
qchemical = -qwater

21. Example 3:
The specific heat of gold is J/g°C. How much heat would be needed to warm g of gold from 25°C to 100°C?
2400J

22. Homework
Calorimetry Worksheet

23. Heat of Fusion (Hf) /Heat of Vaporization(Hv)
Fusion means melting/freezing
Vaporization means boiling/condensing
Hf and Hv - amount of energy needed to melt/freeze or boil/condense 1g of a substance
Different for every substance – look on reference tables
Q = mHf
Q = mHv

24. Examples:
Calculate the mass of water that can be frozen by releasing J.
Calculate the heat required to boil 8.65 g of alcohol (Hv = 855 J/g).
Calculate the heat needed to raise the temperature of 100. g of water from 25 C to 63 C .

25. Phase Change Diagram
The flat points represent a phase change – temperate does not change while a phase change is occurring even though heat is being added.
Diagonal points represent the 3 phases