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Lecture 1

CHM 1311 Lecture Notes - Lecture 1: Sodium Hydroxide, Nitric Acid, Jmol


Department
Chemistry
Course Code
CHM 1311
Professor
Darrin Richeson
Lecture
1

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“...BUT A HOT TEMPER
LEAPS O’ER A COLD DECREE”
Introduction:
In this lab, several different experiments are completed in order to calculate the
enthalpies of various types of reactions. From these reactions, we calculate the specific
and approximate molar mass of a metal, enthalpy of neutralization of two acids with a
base, and the enthalpy of solution of an unknown salt. When needed to find the energy
needed to change the heat of a product or enthalpy, we use
q= mcT [1]
where m is mass of product, c is heat capacity, and T is change in temperature. With
known energy needed to change the known temperature, we can figure out how much
energy we lost from the metal when it gave it to the system to change the temperature by
using
-q(metal) = q(water) [2].
It is possible to estimate the molar mass of a metal once the specific heat capacity of that
metal is known by using
CmetalxMMmetal~25’C [3]
In the neutralization, once the energy used is found by using [1] we can find the enthalpy
of reaction per mole of substance by using
H = qn/nx [4].
The theory that is basis for this experiment is that energy is always constant but simply
transfers energy between items through heat, chemical, light, sound and motion. By using
a calorimeter, we can ensure that all the heat and chemical energy transfer occurring in
the system, stays in the system and isn’t lost into the environment. This will give us the
best possible results in determining the true transfer in energy.
Procedure:
As described in lab Manual (“...BUT A HOT TEMPER LEAPS O’ER A COLD
DECREE, Dr. Rashmi Venkateswaran, Exp. 1, Pg. 34)
Observations:

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Experiment: 1 Enthalpy of Metal
Trial # 1 2
Metal Zn Zn
m of Metal (g) 10.559 10.8643
Volume of H20 (mL) 20 20
m of Calorimeter w/
H20 (g) 26.79 27.13
Temp of Metal (C) 100 100
Temp Change of H20 3.3 3.1
Energy Gained by
H20 (J) 265.8 254.1
Temp Change of Metal
(C) -72.6 -72.4
Heat capacity of Metal 0.347 0.323
Approx Molar Mass of
Zn (g/mol) 72.05 77.39
Percent Error 10.2 18.0
Temps of H20: 1st
Minute (C) 23.6/ 23.8 24.1/ 24.2
2nd Minute 23.9/ 24.0 24.3/ 24.4
3rd Minute 24.1/ 24.1 24.5/ 24.5
Temps after Zn is
Added: 4th minute (C) 27.5/ 27.3/ 27.5 27.7/ 27.6/ 27.6
5th minute 27.5/ 27.5/ 27.4 27.6/ 27.6/ 27.7
6th minute 27.4/ 27.4/ 27.4 27.7/ 27.7/ 27.7
7th minute 27.4/ 27.4/ 27.4 27.6/ 27.6/ 27.6
- Temperature quickly increased as soon and the Zn was added
- In both cases, the temperature it first increased to was roughly the temperature it
stayed at
Experiment 2: Enthalpy of Neutralization HNO3
Trial # 1 2
Acid HNO3 HNO3
Concentration of
HNO3 1.1 mol/L 1.1 mol/L
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