H for each reaction studied will be calculated in units of
kJ/mol of NaOH. As discussed in the “Introduction” section the
Δ
H for the reaction is
identical to the heat flow or “q” for the reaction since the reactions are being
conducted at constant pressure conditions.
In general: q = mass × specific heat ×
Δ
T
Since all the reactions in this experiment are being conducted in an aqueous
medium, the specific heat will be assumed to be the same as the specific heat of
water, which is 4.18
Joules
gram
!
C
.
The heat changes in this experiment involve three different components: 1) the
chemical reaction 2) the aqueous medium and 3) the calorimeter.
q
reaction
+ q
water
+ q
calorimeter
= 0
q
reaction
= -(q
water
+ q
calorimeter)
A second assumption that will be made is that q
calorimeter
is negligible and therefore
can be ignored from these calculations. Therefore:
q
reaction
= -q
water
= -(mass
water
× specific heat
water
×
Δ
T
water
)
A third assumption that will be made in these calculations is that the density of the
solution is the same as the density of water, which is 1.00 grams/mL. Therefore the
mass of the water in each reaction is the same as the volume of the water.
A fourth assumption that will be made in these calculations is that when combining
solutions the total final volume is the same as the sum of the volumes of the
individual solutions.

8
R
EACTION
1
Mass of water
= __________________ grams
Δ
T = T
f
– T
i
= ______________________°C
Specific heat
= 4.18
Joules
gram
!
C
q
water
(Joules)
=
q
water
(kJ)
=
Moles of NaOH
=
q
water
(kJ/mol)
=
q
reaction
(kJ/mol)
= _________________________________
=
Δ
H
1
R
EACTION
2
Mass of water
= __________________ grams
(remember to include the ~ 2 grams of solid NaOH)
Δ
T = T
f
– T
i
= ______________________°C
Specific heat
= 4.18
Joules
gram
!
C
q
water
(Joules)
=
q
water
(kJ)
=
Moles of NaOH
=
Moles of HCl
=
q
water
(kJ/mol)
=
q
reaction
(kJ/mol)
= _________________________________
=
Δ
H
2

9
R
EACTION
3
Mass of water
= __________________ grams
Δ
T = T
f
– T
i
= ______________________°C
Specific heat
= 4.18
Joules
gram
!
C
q
water
(Joules)
=
q
water
(kJ)
=
Moles of NaOH
=
Moles of HCl
=
q
water
(kJ/mol)
=
q
reaction
(kJ/mol)
= _________________________________
=
Δ
H
3
E
VALUATING THE VALIDITY OF
H
ESS
’
S LAW
Measured value of
Δ
H for Reaction 3 = ______________________ (same as
Δ
H
3
above)
Value of
Δ
H for Reaction 3 based on Hess’s law =
Δ
H
2
–
Δ
H
1
= _____________________
Percent error in the calculated value compared to the measured value: (show
calculation below)
Also write equations to show how reactions 1 and 2 will be combined to obtain
reaction 3:

10
R
EACTION
4 (
SAME AS
R
EACTION
1)
Mass of water
= __________________ grams
Δ
T = T
f
– T
i
= ______________________°C
Specific heat
= 4.18
Joules
gram
!
C
q
water
(Joules)
=
q
water
(kJ)
=
Moles of NaOH
=
q
water
(kJ/mol)
=
q
reaction
(kJ/mol)
= _________________________________
=
Δ
H
4
R
EACTION
5
Mass of water
= __________________ grams
(remember to include the ~ 2 grams of solid NaOH)
Δ
T = T
f
– T
i
= ______________________°C
Specific heat
= 4.18
Joules
gram
!
C
q
water
(Joules)
=
q
water
(kJ)
=
Moles of NaOH
=
Moles of CH
3
COOH
=
q
water
(kJ/mol)
=
q
reaction
(kJ/mol)
= _________________________________
=
Δ
H
5

11
R
EACTION
6

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- Winter '10
- Fisher
- Chemistry, Enthalpy, Calorimetry, Reaction