1. Thermochemistry Purpose of the Experiment (Heat of Reaction)
Determine the heat of neutralization for
the reaction of various acids and bases.
Determine the heat of fusion of ice.

2. P = pressure of the system
What is the Heat of Reaction?
Definition of Enthalpy
Thermodynamic Definition of Enthalpy (H):
H = E + PV
E = energy of the system
P = pressure of the system
V = volume of the system

3. At Constant Pressure
Recall, by definition a change in energy equals heat transferred (q) plus work (w):
E = q + w
Consider a process carried out at constant pressure. At constant pressure, work involves only a change in volume. We can then substitute -PV for w.
E = qp - PV
Then if we want to solve for the heat transferred, qp, at constant pressure, we simply rearrange the equation.
qp = E + PV

4. Enthalpy = Heat Transferred
Recall our original definition of enthalpy:
H = E + PV
Then for a change in enthalpy:
H =  E + (PV)
If we set P constant, then:
H =  E + P  V
Since
qp = E + PV
Then
H = qp
The change in enthalpy,  H, is then equal to the heat transferred at constant pressure, qp.

5. H = H products – H reactants
In a chemical reaction
H = H products – H reactants
If H >0, then qp >0
The reaction is Endothermic.
Heat goes from the surroundings into the system.
If H <0, then qp <0
The reaction is Exothermic.
Heat goes from the system into the surroundings.
An example of an exothermic reaction:

6. Heat Capacity, C
“C” is an extensive property; so a large object has a larger heat capacity than a small object made of the same material.
Using the Equation:
Looking at the figures on the left, it can be seen that the temperature change is constant, but the heat absorbed by the larger object is greater.
This results in a larger heat capacity for the larger object because more heat is absorbed.

7. Specific heat capacity: The energy (joules) required to raise the temperature of 1 gram of substance by 1C
Unit: J g-1K-1 or J g-1 1C-1
Molar heat capacity: The energy (joules) required to raise the temperature of 1 mol of substance by 1C
Unit: J mol-1 K-1 or J mol-1 1C-1

8. Substance
Specific Heat, Cs
(cal/gram°C)
(J/kg °C)
Pure water
1.00
4,186*
Wet mud
0.60
2,512
Ice (0 °C)
0.50
2,093
Sandy clay
0.33
1,381
Dry air (sea level)
0.24
1,005
Quartz sand
0.19
295
Granite
294
1 calorie = joules
*The high heat capacity of water makes it ideal for storing heat
in solar heating systems.

9. Neutralization The reaction between an acid and a base
which results in a salt plus water.
For example, hydrochloric acid and sodium hydroxide:
HClaq + NaOHaq  NaClaq + H2O
acid + base  salt water
Another example, cyanic acid and a hydroxide ion. If we use KOH, what salt will form?

10. Heat of Neutralization
Net ionic equation for neutralization:
H+(aq) + OH-(aq)  H2O(l)
Energy released by reaction = Energy absorbed by solution
Specific heat capacity, Cs, is defined as the quantity of heat transferred, q, divided by the mass of the substance times the change in temperature. A value of Cs is specific to the given substance.
Cs = q / [(mass) (Tfinal-Tinitial)]
This can then be rearranged to solve for the heat transferred.
q = (mass) Cs (Tfinal-Tinitial)

11. Enthalpy of Fusion (Melting)
Enthalpy of Fusion is defined as the heat that is absorbed when the melting occurs at constant pressure. If the substance freezes, the reaction is reversed, and an equal amount of heat is given off to the surroundings; i.e., ΔHfreez = - ΔHfus
solid
liquid
Melting (fusion) is an endothermic process

12. Calorimetry Science of measuring heat based on observing the
temperature change when a
body absorbs or loses
energy as heat.
A calorimeter can be created by doing something as simple as inserting one Styrofoam cup inside another.

13. Heat lost by hot object = Heat gained by cold water
Calorimetry
A Calorimeter may be used to determine the Heat Capacity, Cs, of a material by measuring the temperature change when a known mass of the material at a higher temperature is placed in a known mass of water, usually at room temperature, and the system is allowed to reach a final intermediate temperature.
Heat lost by hot object = Heat gained by cold water
(mass)material Cs material (Tfinal-Tinitial)material = -(mass)water Cs water (Tfinal-Tinitial)water
Note: The heat capacity is related to the atomic mass and the intermolecular forces in the material.
is a mnemonic – an easy way to remember mCsT

14. Calorimetry
A Calorimeter may be used in a similar manner to determine the enthalpy change associated with other processes, such as:
Chemical reactions* (bond energies)
Phase changes* (intermolecular forces)
Mixing (intermolecular forces)
Solvation (intermolecular forces)
*These are the processes you will be learning today.

15. An example of an exothermic reaction from the S&T mining dept:
Have you ever wondered about how they determine the calories in food? They use a Bomb Calorimeter. It can be used to determine the caloric value of food and of fuels, by burning them in excess oxygen and measuring the amount of heat evolved. A basic combustion reaction:
CxHy + O2(excess) --> x CO2 + y/2 H2O + heat
Bomb Calorimeter
An example of an exothermic reaction
from the S&T mining dept:

16. The Computer Display Setup for Today’s Experiments
If probe displays less than 15 oC, notify your TA.
Parameters:
Temperature: oC
Time: seconds
(Check: Probe should display oC resting on lab bench
and should read higher when warmed by hand.)

17. The Heat of Neutralization Experiments
Mixture not stirred fast enough – Resulting line is not vertical.
Reaction is completed,
heat released, begin
slow cooling to ambient
HCl and NaOH mixed,
reaction begins
Temperature change is important. Exact time is not important.
Temperature will drift toward ambient before and after reaction
Transition will be faster if NaOH is added rapidly and well stirred.
(That is, you will have a more nearly vertical temp. rise.)

18. The Heat of Fusion Experiment
Mixture not stirred fast enough – Resulting line is not vertical.
Ice cube added
Melting complete,
begin slow warming
IMPORTANT: a.) Use only 1 ice cube; b.) the entire cube must melt.

19. Use distilled water from carboys*,
Checkout
1 - Calorimeter (Thermos)
1 - Styrofoam Cup
1 – 100 ml Graduated Cylinder
– When all experiments are completed, rinse with water and
return all 3 items to the stockroom.
Reagents in Lab
(Record concentration from carboys onto datasheets.
Note: Concentrations may vary from one class to the next.)
_____M HCl (strong acid)
_____M CH3CO2H (weak acid)
_____M NaOH (strong base)
Important:
Use distilled water from carboys*,
NOT from the tap.
(*Distilled water from the tap is normally not at room temp.)

20. For April 7-9 Liquid waste labeled “Heat of Neutralization” Hazards
HCl, strong acid, corrosive
CH3CO2H, weak acid, corrosive
NaOH, strong base, corrosive
Waste
Liquid waste labeled “Heat of Neutralization”
For April 7-9
Due: Thermochemistry pp in the lab packet
and a calculations page
and Dimensional Analysis #4-5 in the first book*
4.1 & 4.2: a, c, f, & h only; 5.1 – 5.4: a & c only
Read over: “Antacid Analysis”
pp in the lab packet
*Lost your 1st book? Go to