The Standard Enthalpy of Solution, DH°sol, 298, is the heat change which takes place when one mole of a solute is completely dissolved in a solvent to form a solution of concentration 1 mol dm-3, measured under standard conditions. Enthalpy of Solution can be measured experimentally. It can also be calculated; it is the sum of two imaginary steps: the reverse of the lattice enthalpy plus the sum of the hydration enthalpies of the ions.

1. The coffee cup bomb calorimeter
By:Dr. Robert D. Craig, Ph.D

2. Page 287 only
• A set of nested coffee cups is a good constant
pressure calorimeter
• http://smithecta.weebly.com/chapter-9---
heat.html
• http://snapguide.com/david-shipp/
• http://web.lemoyne.edu/~giunta/chm151L/ca
lorimetry.html

3. Today’sAgenda
• To determine the specific heat of a metal
• To determine the enthalpy of neutralization
for a strong acid-strong base reaction
• To determine the enthalpy of solution for the
dissolution of a salt

4. Introduction from Your text
• Accompanying all chemical and physical
changes is a transfer of heat (energy); heat
may be either evolved (exothermic) or
absorbed (endotherminc) .

5. heat (energy) evolved (exothermic)

6. heat (energy) absorbed
(endotherminc) .

7. NH4NO3 (c, IV) in water at 298.15 K to be
ΔHo = 25.41 kJ mol−1.

8. A calorimeter . . . .hold heat well
• A calorimeter is the laboratory apparatus that
is used to measure the quantity and direction
of heat flow accompanying a chemical or
physical change.

9. A professional one used in industry

10. Measures heat content . .

11. Entalphy . . A function of state
• The heat change in chemical reactions is
quantitatively expressed as the enthalpy (or
Heat) of reaction H, at constant pressure

12. negative for exothermic
• H values are negative for exothermic
reactions and positive for endothermic
reactions.

13. a state function –independent of path

14. a state function –independent of path

15. The classic things today . .
• Three quantitative measurements of heat are
detailed in this experiment:
• 1. Measurements of the specific heat of a
metal,
• 2. the heat change accompanying an acid-base
reaction,
• 3. and the heat change associated with the
dissolution of a salt in water.

16. in joules,J
The energy (heat, expressed in joules,J) required
to change the temperature of one gram of a
substance by 1oC is the specific heat of that
substance SI units:

17. The specific is specific to all metals

18. Intensive properties-How much ???
• Intensive properties (temperature, pressure)
do not depend upon the sample size.

19. Extensive-not how much

20. Confusing. . .must check units
• Intensive
property**
• Specific heat capacity
at constant volume ======J/(kg·K)
• extensive
property**
• heat capacity
at constant volume ======J/K

21. heat capacity as an intensive property
• heat capacity as an intensive
property, i.e., independent of the size of a
sample, are the molar heat capacity, which is
the heat capacity per mole of a pure
substance, and the specific heat
capacity, often simply called specific
heat, which is the heat capacity per unit mass
of a material.

22. (25.2)
• Or rearranging for energy,

23. T is the temperature change
• T is the temperature change of the substance.
• Although the specific heat of a substance changes
slightly with temperature, for our purposes, we
assume it is constant over the temperature changes
of this experiment.

24. • The specific heat of a metal that does not
react with water is determined by heating a
measured mass of the metal, M to a known
(higher) temperature placing it into a
measured amount of water at a known (lower)
temperature measuring the final equilibrium
temperature after the two are combined.

25. final equilibrium temperature after the
two are combined

26. Page 288
• The following equations, based on the law of
conservation of energy (insert NoW-
Rob!!!!!!!!!)
•

27. specific heat of a metal
• Show the calculations for determining the
specific heat of a metal. Considering the
direction of energy flow by the conventional
sign notation energy loss being “negative” and
energy gain being “positive” then

28. (25.3)
--Energy Lost (-J) by the metal =
Energy (+J) gained by water

29. specific heat of a metal
Substituting and rearranging, We have
-specific heat x mass(M) x DT = specific heat
(H20) x mass (H20) x DT (H20)

30. This is (25.4)
This is equation (25.4) Rearranging equation
(25.4) , we solve for the specific heat of the
Metal as:

31. (25.5)
+specific heat x mass(M) x DT =
(-) specific heat (H20) x mass (H20) x DT (H20)
• mass(M) x DT

32. (25.6)
• In the equation, the temperature change for
either substance is defined as the difference
between the final temperature Tf, and the
initial temperature, Ti, of the substance
T-= Tf - Ti

33. T-= Tf - Ti
• These equations assume no heat lost to the
calorimeter when the metal and the water are
combined. The specific heat of water in 4.184
J/g.oC

34. .
• In addition to using the calorimeter
properly, key techniques for obtaining
accurate results are starting with a dry
calorimeter, measuring solution volumes
precisely, and determining T accurately.
Careful experimenters deal with the first two
items easily.

35. • The last is somewhat more difficult. The
change in temperature is determined by
measuring the initial temperature, T1, of the
reactants, and the maximum
temperature, T2, of the contents of the
calorimeter during the exothermic reaction.

36. .
• . The determination of a precise value for T2 is
complicated by the fact that a small heat
exchange occurs between the surroundings and
the contents of the calorimeter, both during the
reaction and after its completion. The rate of
exchange depends on the insulating properties of
the calorimeter and on the rate of stirring. A
correction for this heat loss is made by an
extrapolation of a temperature vs. time curve
(see Figure 1 in your lab manual).

37. .
• The rate of exchange depends on the
insulating properties of the calorimeter and
on the rate of stirring. A correction for this
heat loss is made by an extrapolation of a
temperature vs. time curve (see Figure 1 in
your lab manual).

38. Calorimeter video one-
peterjackson118
• http://www.youtube.com/watch?v=WfO2sY-
GJec&list=UUSnmgHe14lSSjaUfrtFdPGA&inde
x=5&feature=plcp

39. Figure 2. Graph of temperature as a function of time for an
exothermic reaction in a perfect calorimeter .

40. no calorimeter is perfect!!!!
• Unfortunately, no calorimeter is perfect, and
instantaneous mixing and reaction are not
always achieved (even with efficient
mixing). In this case, the graph of
temperature as a function of time looks more
like the figure above

41. .
• We can still find ΔT, but now we must
extrapolate back to when the solutions were
mixed (time, t, equals zero). This is most
easily done by performing a linear regression
on the sloped portion of the graph (where, for
exothermic reactions, heat is leaking out of
the calorimeter) and obtaining Tfinal from the
y-intercept.

42. Put 3 caution slides here

43. Part B