Sultan Qaboos University
Collage of Science
Department of Chemistry
Physical Chemistry Laboratory (CHEM3335)
THERMODYNAMIC
PROPERTIES OF
WATER
Name:Al Hamdani.
ID:
Date: 27/4/2010.
0
Objective:
The purpose of this experiment is to study the thermodynamic properties of
water by determining the enthalpy.
Introduction:
Thermodynamic is the study of the heat, work, energy and the changes they
produce in the state of the system. By knowing the thermodynamic properties
e.g. heat capacity(C), change in enthalpy (∆H) and many other properties we
can measure the energy change of the system.
Water (H2O) is a fundamental features in our life. It has a special
characteristics due to dipolar molecular structure. The change of water into
different states include either absorb heat(endothermic process) as in this
chemical equation:
(melting)
H2O(s)→H2O(l)
Or release heat(exothermic process) as in this chemical equation:
(freezing) H2O(s)→H2O(l)
The specific heat is the amount of heat in joule per gram required to raise the
temperature by one degree Celsius. forwater the specific heat is 4.186J/g 0C
which is higher than any other common substance.
From the product of the average specific heat capisity cp and the Celsius
temperature .we can find the enthalpy relative to 0 0C for water which is the
energy needed to heat water.
The enthalpy conservationon mixing(A+B)is (ab)in KJ/Kg is defined by
1
( A)  ( a )  ( B )  (b)  ( A  B )  ( ab)
sin ce A is liquid water

 ( a ) 
C
T
p1 a
0
sin ce below 80C , CP indepenent of temperature so
 ( a )  CP1Ta
so  ( ab)  CPTab
(1  B / A)Tab 
 (b) B
  Ta
CP1
A
where the plot of (1  B / A)Tabversus B / A will give us linear
graph with a slope 
 (b)
and the int ercept  Ta
CP1
Experimental:
Apparatus and chemicals:
*Volumetric flask
*water bath
*Dewar flask
*Balance
*plastic cup
*device to measure the temperature.
Condition:
*Room Temperature
*Pressure= 1 atm
2
Procedure:
1-pour 250ml of distilled water in volumetric flask and put it in water
bath and record the temperature of the water(Ta).
2-weigh10.0g of ice and then put it inside the provided dewar flask and
you must be accurate and don not touch the ice by your finger.
3-pour the prepared water in step1in the dewar flask and stir it untind
all the ice melts and then record the temperature of the mixture(Tab).
4-repeats steps 2,3by using amount of ice (20,30,40,50,55,60,65,70,75)
Results:
A(g)
Table1: the result
that we got it from
our experiment.
B(g)
B/A
Tab
1+B/A
(1+B/A)*Tab
Ta
247.51
10.08
0.040726
30.02
1.040726
31.2
35
247.23
20.03
0.081018
27.2
1.081018
29.4
35
247.27
30
0.121325
23.3
1.121325
26.1
35
247.31
40.1
0.162145
20.9
1.162145
24.3
35
247.23
50.28
0.203373
17.8
1.203373
21.4
35
247.29
55.14
0.222977
16.2
1.222977
19.8
35
247.67
60.04
0.242419
14.5
1.242419
18.0
35
246.82
65.33
0.264687
13.9
1.264687
17.6
35
247.58
70.1
0.283141
12.2
1.283141
15.7
35.1
247.42
75.05
0.30333
12.1
1.30333
15.8
34.9
3
B/A vs (1+B/A)*Tab
35.0
(1+B/A)*Tab
30.0
25.0
20.0
15.0
10.0
5.0
0.0
0
0.05
0.1
0.15
0.2
0.25
0.3
B/A
Fig(1) shows the plot of (1+B/A)Tabvs
B/A
Calculations:
Mass of water(A)
Mass of ice(B)
B 10.08

 0.04073 g
A 247.51
B
1   1  0.04073  1.04073 g
A
B
(1  )Tab  1.04073 g  30.02  C  31.24 g .  C
A
B
(b) B
(1  )Tab 
  Ta
A
C P1
A
(b)
 0.04073 g  35.0  C
4.2 KJ / Kg. C
(b)  387 J
if we det er min e the enthaply change from the det er min e slop :
(b)
 62.9138
C P1
31.24 g . C 
(b)  264 KJ / Kg
4
0.35
Discussion
In this experiment we determined the enthalpy which is needed to melt
the ice by calculating the slop of the graph (1+B/A)TabvsB/A. we
notice that there is different between the measured value and the
literature value that is indicated to uncertainty in our result, there is
some error during the experiment.
Answers of questions:
a- The different sign of vap and freeze because the system gains
energy to break the intermolecular force of water to evaporate .But it
loses energy to make the bonds and solidifying the water.
b- we use distilled water to obtain pure ice because the impurities affect
the freezing point of water.
c-we don not use our hand to transfer the ice because the heat can flow
from our hand and affect the Tb, so it will effect and it may
contaminate with ice and affect the mass.
Error analysis:
Slop is -62.9138± 1.991735
Intercept is 34.0431± 0.418415
The source of error which occur in the experiment is
1- Inaccuracy in reading the temperature
2- Exceeded the time given (20-30s) for weighing the ice, so the ice
started to melt and this is leads to affect the results.
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