1. Warm-up
Sketch an energy diagram for the hydrolysis of water into Hydrogen gas and Oxygen gas
Energy level of water: 60 kJ, Activation Energy 500 kJ
Get enthalpy from previous notes.
Is the reaction endo/exothermic?

2. Ch. 17.2 Calorimetry and Heat of Rx

3. Classes of Energy
Kinetic Energy: energy stored in motion, speed, radiation, sound
Potential Energy Q: energy stored in position ,includes chemical energy, energy stored in chemical bonds

4. Energy Transfers

5. Calorimetry measures the heat released or absorbed by
Objects b) Rx with unknown C!!!
Using an insulated chamber (Thermos) where a) or b)
transfer their heat
onto water

6. Energy Units Joules, calories, Calories 1 cal = 4.18 J
1000 cal = 1 kcal = 1Cal (big cal)
Big Calories are used for food energy

7. Thermoenergy Classes
Heat Q (physics) = general heat stored in a system, calorimeter, metal shot, water
Enthalpy H (chemistry) chemical energy stored in molecules, used for Rx, ∆ H change in Enthalpy
Unit: Joules J, or calories cal

8. Calculating Heat Change in a Calorimeter
Q = m x C x ∆T
C water: ∆T: Temp difference
CH2O= 4.18 J/goC Tfinal – T initial
Mass water
1 ml = 1g

9. Interpreting Calorimeter data
gives indirect evidence of the Rx or the property of the objects
The water heated up: Rx was exo
The water cooled down: Rx was endo

10. In a calorimeter, a chemical Rx A + B → C changed the temp of 50 ml of surrounding water from 50o C to 20o C. 1) Calculate the change of enthalpy of the Rx 2) Write the thermochemical Rx
Q= m x C x Δ T CH20 = 4.18 J/g C
m = 50 ml = 50 g
Δ T =20oC - 50oC = -30oC cooled down
Q = 4.18 J/g C x 50 g x -30o C = -6,270 J
Q Rx = + 6,270 J endothermic Rx!
A + B + 6,270 J = C

11. Water got hotter: exothermic A + 2 B = 3C + 1,463 J
50 ml of an aqueous reaction A + 2B → 3C takes place in a calorimeter where the water temp changed from 25oC to 32oC What is the change in enthalpy ∆H of the Rx? Rewrite the reaction and include the enthalpy.
ΔT = = +7oC
Q= m x C x ΔT = 50 g x 4.18 J/goC x 7oC
Q water= +1,463 J
Q Rx = -1,463 J
Water got hotter: exothermic
A + 2 B = 3C + 1,463 J

12. ∆H of Combustion Rx: Hydrogen: H2 ΔH Rx: -286 kJ/mol
(Water: H2O ΔH Rx: +286 kJ/mol)
Ethanol C2H5OH ΔH Rx: kJ/mol
Propane C3H ΔHRx : kJ/mol
Octane C8H ΔHRx : kJ/mol
Glucose C6H12O ΔH Rx: -2808kJoules/mol
Synthesis is anabolic and endothermic (+)
Digestion/combustion is catabolic and exothermic (-)

13. Practice C6H12O6 + 6O2 → 6 CO2 + 6 H2O + 2808 kJ
Is this reaction endo or exothermic?
How much heat is released when 2.38 moles of Glucose are combusted?
Pathway: Moles → Heat
2.38 moles x _-2808 kJ __= kJ
mole C6H12O6

14. a) Write the balanced thermochemical synthesis Rx for water Use a) to calculate the amount of heat needed/released when 20 g of water are produced
a) H2 + O2 → 2H2O +572 kJ
Mass → moles → heat
20 g x 1 mole x kJ = kJ
moles
Synthesis of water is exothermic so released.