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14.E: Thermochemistry (Exercises)

Last updated

Mar 3, 2021
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- 14.6: Applications of Thermochemistry
- 15: Thermodynamics of Chemical Equilibria

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13.2: The First Law of Thermodynamics

13.3: Molecules as energy carriers and converters

After going through combustion in a bomb calorimeter a sample gives off 5,435 cal. The calorimeter experiences an increase of 4.27°C in its temperature. Using this information, determine the heat capacity of the calorimeter in kJ/°C.

Q13.5.2

Referring to the example given above about the heat of combustion, calculate the temperature change that would occur in the combustion of 1.732 g $C_{12}H_{22}O_{12}$ in a bomb calorimeter that had the heat capacity of 3.87 kJ/°C.

Q13.5.3

Given the following data calculate the heat of combustion in kJ/mol of xylose, $C_{5}H_{10}O_{5}$ (s), used in a bomb calorimetry experiment: mass of $C_{5}H_{10}O_{5}$ (s) = 1.250 g, heat capacity of calorimeter = 4.728 kJ/°C, Initial Temperature of the calorimeter = 24.37°C, Final Temperature of calorimeter = 28.29°C.

Q13.5.4

Determine the heat capacity of the bomb calorimeter if 1.714 g of naphthalene, $C_{10}H_{8}$ (s), experiences an 8.44°C increase in temperature after going through combustion. The heat of combustion of naphthalene is -5156 kJ/mol $C_{10}H_{8}$ .

Q13.5.5

What is the heat capacity of the bomb calorimeter if a 1.232 g sample of benzoic acid causes the temperature to increase by 5.14°C? The heat of combustion of benzoic acid is -26.42 kJ/g.

S13.5.1

Use equation 4 to calculate the heat of capacity:

$q_{calorimeter} = \; heat \; capicity \; of \; calorimeter \; x \; \Delta{T}$

5435 cal = heat capacity of calorimeter x 4.27°C

Heat capacity of calorimeter = (5435 cal/ 4.27°C) x (4.184 J/1 cal) x (1kJ/1000J) = 5.32 kJ/°C

S13.5.2

The temperature should increase since bomb calorimetry releases heat in an exothermic combustion reaction.

Change in Temp = (1.732 g $C_{12}H_{22}O_{11}$ ) x (1 mol $C_{12}H_{22}O_{11}$ /342.3 g $C_{12}H_{22}O_{11}$ ) x (6.61 x 10³ kJ/ 1 mol $C_{12}H_{22}O_{11}$ ) x (1°C/3.87kJ) = 8.64°C

S13.5.3

[(Heat Capacity x Change in Temperature)/mass] =[ ((4.728 kJ/°C) x(28.29 °C – 24.37 °C))/1.250 g] = 14.8 kJ/g xylose

$q_{rxn}$ = (-14.8 kJ/g xylose) x (150.13 g xylose/ 1 mol xylose) = -2.22x10³ kJ/mol xylose

S13.5.4

Heat Capacity = [(1.714 g $C_{10}H_{8}$ ) x (1 mol $C_{10}H_{8}$ /128.2 g $C_{10}H_{8}$ ) x (5.156x10³ kJ/1 mol $C_{10}H_{8}$ )]/8.44°C = 8.17 kJ/ °C

S13.5.5

Heat Capacity = [(1.232 g benzoic acid) x (26.42 kJ/1 g benzoic acid)]/5.14°C = 6.31 kJ/ °C

13.1: Energy, heat and work

13.2: The First Law of Thermodynamics

13.3: Molecules as energy carriers and converters

13.4: Thermochemistry

13.5: Calorimetry

Q13.5.1