1. Calorimetry

2. Calorimetry
Calorimetry - the accurate and precise measurement of heat change for chemical and physical processes.
The device used to measure the absorption or release of heat in chemical or physical processes is called a Calorimeter

3. Calorimetry
Foam cups are excellent heat insulators, and are commonly used as simple calorimeters

4. A Cheap Calorimeter

5. For systems at constant pressure, the heat content is the same as a property called Enthalpy (H) of the system

6. Calorimetry Changes in enthalpy = H
q = H These terms will be used interchangeably in this textbook
Thus, q = H = m x C x T
H is negative for an exothermic reaction
H is positive for an endothermic reaction

7. Calorimetry
Calorimetry experiments can be performed at a constant volume using a device called a “bomb calorimeter” - a closed system

9. In terms of bonds C O O C O Breaking this bond will require energy. C
Making these bonds gives you energy.
In this case making the bonds gives you more energy than breaking them.

10. Exothermic The products are lower in energy than the reactants
Releases energy
2Al (s) + 3Cl2 (g) --> 2 AlCl3 (s) kJ
∆H=1408 kJ

11. C + O2 ® CO2
+ 395 kJ
Energy
Reactants
Products
C + O2
395kJ
C O2

12. Endothermic The products are higher in energy than the reactants
Absorbs energy
2 H2O kJ > 2 H2 + 1 O2 (g)
∆H = kJ

13. CaCO3 + 176 kJ ® CaO + CO2 CaCO3 ® CaO + CO2 Energy Reactants Products

14. Chemistry Happens in MOLES
An equation that includes energy is called a thermochemical equation
CH4 + 2O2 ® CO2 + 2H2O kJ
1 mole of CH4 releases kJ of energy.
When you make kJ you also make 2 moles of water

15. What is the molar enthalpy of CO2 (g) in the reaction for the burning of butane below?
2 C4H O2  8 CO2 +10 H2O
∆H=-5315 kJ
Answer: Molar enthalpy is the enthalpy change in equation divided by the balance of CO2
Molar enthalpy, ∆H substance = 5315 kJ ÷ 8 mol
= 664 kJ / mol.

16. For each of the following rewrite the equation in " H " notation, for one mole of the underlined substance.
Fe2O3 (s)+3CO(g)→3CO2(g)+2Fe(s)+25kJ
Answer:
1/3 Fe2O3 (s)+CO(g)CO2(g)+2/3 Fe(s)
∆H = KJ 
4 NH3(g)+5O2 (g)→4 NO(g)+6H2O(l)+1170kJ   

17. 2 HCl (g)+96 KJ → H2 (g)+Cl2 (g)
N2 (g)+3 H2 (g) → 2 NH3 (g)+92 KJ
2 CO2 (g)+566 KJ →2 CO (g)+ O2 (g)
4 Al (s) +3 O2 (g) →2 Al2O3 (s)+3360 KJ

18. Thermochemical Equations
A heat of reaction is the heat change for the equation, exactly as written
The physical state of reactants and products must also be given.
Standard conditions for the reaction is kPa (1 atm.) and 25 oC

19. CH4 + 2 O2 ® CO2 + 2 H2O kJ
If grams of CH4 are burned completely, how much heat will be produced?
1 mol CH4
802.2 kJ
10. 3 g CH4
16.05 g CH4
1 mol CH4
= 514 kJ

20. How many grams of water would be produced with 506 kJ of heat?
CH4 + 2 O2 ® CO2 + 2 H2O kJ
How many liters of O2 at STP would be required to produce 23 kJ of heat?
How many grams of water would be produced with 506 kJ of heat?

21. How much heat will be released if 65 grams of butane is burned in a lighter according the equation:
2 C4H O2  8 CO2 +10 H2O
∆H=-5315 kJ
= kJ
= 3.0 MJ

22. Calculate the heat released when 120 grams of Iron (III) oxide is formed by the following equation 
2 Fe2O3 (s) → 4 Fe(s)+3 O2 (g)
∆H=1625 kJ
= kJ
= 610 kJ

23. Q = n ∆H (substance)
Where n = # of moles

24. What mass of carbon dioxide must form to create 1200 kJ of heat when the following reaction occurs?
C6H12O6(s)+6O2(g)→6CO2(g)+6H2O(l) 
∆H=- 2808kJ
Answer: 110 grams

25. 3) What mass of oxygen is needed to completely react and release 550 kJ of heat in the following reaction?
4Fe (s)+3O2 (g) → 2 Fe2O3 (s)
∆H= kJ
Answer: 32 grams

26. Summary, so far...

27. Enthalpy
The heat content a substance has at a given temperature and pressure
Can’t be measured directly because there is no set starting point
The reactants start with a heat content
The products end up with a heat content
So we can measure how much enthalpy changes

28. Enthalpy Symbol is H Change in enthalpy is DH (delta H)
If heat is released, the heat content of the products is lower
DH is negative (exothermic)
If heat is absorbed, the heat content of the products is higher
DH is positive (endothermic)

29. Energy
Change is down
DH is <0
Reactants
Products

30. Energy
Change is up
DH is > 0
Reactants
Products

31. Heat of Reaction
The heat that is released or absorbed in a chemical reaction
Equivalent to DH
C + O2(g) ® CO2(g) kJ
C + O2(g) ® CO2(g) DH = kJ
In thermochemical equation, it is important to indicate the physical state
H2(g) + 1/2O2 (g)® H2O(g) DH = kJ
H2(g) + 1/2O2 (g)® H2O(l) DH = kJ

32. Heat of Combustion
The heat from the reaction that completely burns 1 mole of a substance

33. OBJECTIVES:
Classify, by type, the heat changes that occur during melting, freezing, boiling, and condensing.

34. OBJECTIVES:
Calculate heat changes that occur during melting, freezing, boiling, and condensing.

35. Heats of Fusion and Solidification
Molar Heat of Fusion (Hfus) - the heat absorbed by one mole of a substance in melting from a solid to a liquid
Molar Heat of Solidification (Hsolid) - heat lost when one mole of liquid solidifies

36. Heats of Fusion and Solidification
Heat absorbed by a melting solid is equal to heat lost when a liquid solidifies
Thus, Hfus = -Hsolid

37. Heats of Vaporization and Condensation
When liquids absorb heat at their boiling points, they become vapors.
Molar Heat of Vaporization (Hvap) - the amount of heat necessary to vaporize one mole of a given liquid.

38. Heats of Vaporization and Condensation
Condensation is the opposite of vaporization.
Molar Heat of Condensation (Hcond) - amount of heat released when one mole of vapor condenses
Hvap = - Hcond

39. Heats of Vaporization and Condensation
The large values for Hvap and Hcond are the reason hot vapors such as steam is very dangerous
You can receive a scalding burn from steam when the heat of condensation is released!

40. Heats of Vaporization and Condensation
H20(g)  H20(l) Hcond = kJ/mol

41. Heat of Solution
Heat changes can also occur when a solute dissolves in a solvent.
Molar Heat of Solution (Hsoln) - heat change caused by dissolution of one mole of substance
Sodium hydroxide provides a good example of an exothermic molar heat of solution:

42. Heat of Solution NaOH(s)  Na1+(aq) + OH1-(aq) Hsoln = - 445.1 kJ/mol
The heat is released as the ions separate and interact with water, releasing kJ of heat as Hsoln thus becoming so hot it steams
H2O(l)