8. Thermochemistry

Constant-Volume Calorimetry

Calorimetry (Constant-Pressure Calorimeter)

Exactly 1.5 g of a fuel burns under conditions of constant pressure
and then again under conditions of constant volume. In measurement
A the reaction produces 25.9 kJ of heat, and in measurement
B the reaction produces 23.3 kJ of heat. Which measurement
(A or B) corresponds to conditions of constant pressure? Explain.

The heat of combustion of ethanol, C2H5OH(l), is -1367
kJ>mol. A bottle of stout (dark beer) contains up to 6.0%
ethanol by mass. Assuming the density of the beer to be
1.0 g>mL, what is the caloric content due to the alcohol
(ethanol) in a bottle of beer (500 mL)?

Constant-Volume Calorimetry Example 1

When 0.514 g of biphenyl (C12H10) undergoes combustion in a
bomb calorimeter, the temperature rises from 25.8 °C to 29.4 °C.
Find ΔErxn for the combustion of biphenyl in kJ>mol biphenyl.
The heat capacity of the bomb calorimeter, determined in a separate
experiment, is 5.86 kJ/°C.

A 2.20-g sample of phenol 1C6H5OH2 was burned in a bomb
calorimeter whose total heat capacity is 11.90 kJ>°C. The
temperature of the calorimeter plus contents increased from
21.50 to 27.50 °C. (b) What is the heat of combustion per mole of phenol?

From the following data for three prospective fuels, calculate
which could provide the most energy per unit mass and per
unit volume:
Fuel Density at 101.3 kPa (g/cm3) Molar Enthalpyof Combustion (MJ/mol)
Octane, C8H181l2 0.70 at 20 °C -5.53
Liquid Butane, C4H101l2 0.60 at -1 °C -2.88
Liquid hydrogen, H21l2 0.07 at -253 °C -0.29

Under constant-volume conditions, the heat of combustion
of sucrose (C12H22O11) is 16.49 kJ>g. A 3.00-g sample of sucrose
is burned in a bomb calorimeter. The temperature of the
calorimeter increases from 21.94 to 24.62 °C. (a) What is the
total heat capacity of the calorimeter?

Palmitic acid (C16H32O2) is a dietary fat found in beef and butter.
The caloric content of palmitic acid is typical of fats in general.
Write a balanced equation for the complete combustion of
palmitic acid and calculate the standard enthalpy of combustion.
What is the caloric content of palmitic acid in Cal/g? 
The standard enthalpy of formation of palmitic acid
is -208 kJ/mol and that of sucrose is -2226.1 kJ>mol. [Use
H2O(l ) in the balanced chemical equations because the metabolism
of these compounds produces liquid water.]

Constant-Volume Calorimetry Example 2

Under constant-volume conditions, the heat of combustion 
of sucrose (C12H22O11) is 16.49 kJ>g. A 3.00-g sample of sucrose 
is burned in a bomb calorimeter. The temperature of the 
calorimeter increases from 21.94 to 24.62 °C. (b) If the size of the sucrose 
sample had been exactly twice as large, what would the 
temperature change of the calorimeter have been?

The heat of combustion of fructose, C6H12O6, is -2812
kJ>mol. If a fresh golden delicious apple weighing 120 g
contains 16.0 g of fructose, what caloric content does the
fructose contribute to the apple?

Heat of Combustion is the amount of heat released when 1 mole of substance is burned or combusted in a Bomb Calorimeter.

When 0.187 g of benzene, C6H6, is burned in a bomb calorimeter the temperature rises by 3.45 °C. If the heat capacity of the calorimeter is 2.46 kJ>°C, calculate the combustion energy 1∆E2 for benzene in units of kJ/g and kJ/mol.

Thermochemistry | Constant-Volume Calorimeter (Bomb Calorimeter).

Under constant-volume conditions, the heat of combustion of 
naphthalene 1C10H82 is 40.18 kJ>g. A 2.50-g sample of naphthalene 
is burned in a bomb calorimeter. The temperature of 
the calorimeter increases from 21.50 to 28.83 °C. 
(c) Suppose that in changing samples, a portion 
of the water in the calorimeter were lost. In what way, if any, 
would this change the heat capacity of the calorimeter?

A 1.50-g sample of quinone 1C6H4O22 is burned in a bomb 
calorimeter whose total heat capacity is 8.500 kJ>°C. The temperature 
of the calorimeter increases from 25.00 to 29.49°C. 
(b) What is the heat of combustion per 
gram of quinone and per mole of quinone?

(b) Assuming that there is an uncertainty
of 0.002 °C in each temperature reading and that the
masses of samples are measured to 0.001 g, what is the estimated
uncertainty in the value calculated for the heat of
combustion per mole of caffeine?

Determine whether each process is exothermic or endothermic
and indicate the sign of ΔH.
a. dry ice evaporating 
b. a sparkler burning
c. the reaction that occurs in a chemical cold pack used to ice
athletic injuries

 The mass of water must be converted to moles. 

 To convert the mass of water to moles, the mass should be divided by the molar mass. 

 The mass of water needs to be converted to moles to use in the calculation. 

 Heat is released by the system (the water) in this instance. 

The positive sign of &#916;H indicates an endothermic change.

 Enthalpy is an extensive property&#8212; it depends on the amount of material present. 

When water evaporates from a beaker at 25&#x2103;, 44.0 kJ/mol of heat is required. How much heat is required when 10.0 g of water completely evaporates?H2O (l) &#8594; H2O (g); 	&#916;H = +44.0 kJ/mol

Mothballs are composed primarily of the hydrocarbon naphthalene
(C10H8). When 1.025 g of naphthalene burns in a bomb
calorimeter,
the temperature rises from 24.25 °C to 32.33 °C. Find
ΔErxn for the combustion of naphthalene. The heat capacity of
the bomb calorimeter, determined in a separate experiment, is
5.11 kJ/°C.

Constant Volume Calorimetry

Does a measurement carried out in a bomb calorimeter give a value for ∆H or ∆E? Explain.

Chapter 09 - 18 - Constant Volume Calorimetry (Bomb Calorimetry)

CHEMISTRY 101 - Constant volume calorimetry

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[BOOK CHEM] Clutch Version

Hess's Law

Hess's Law involves the use of partial reactions in the determination of the overall enthalpy of reaction.

Nature of Energy

Thermochemistry is the study of matter and energy associated with chemical reactions or physical changes.&nbsp;

Endothermic & Exothermic Reactions

Endothermic and Exothermic Reactions involve the absorbing and releasing of thermal energy respectively.&nbsp;&nbsp;

Heat Capacity

Heat Capacity is the amount of heat required to change the temperature of a substance.&nbsp;

Thermochemical Equations

Thermochemical Equations&nbsp;involve a balanced chemical equation with a given enthalpy value.

Internal Energy

The Internal Energy of a system is the total energy from all forms of kinetic and potential energy.&nbsp;

Kinetic & Potential Energy

Mechanical Energy is the energy associated with an object's velocity (Kinetic Energy) and its position (Potential Energy).&nbsp;

Formation Equations

Formation Equations involve the standard states of elements combining to form 1 mole of product.

Enthalpy of Formation

The Enthalpy of Formation for an element is a key component in determining the enthalpy of reaction.&nbsp;

Thermal Equilibrium

Thermal Equilibrium involves two substances that are in physical contact reaching the same final temperature over time.&nbsp;

Constant-Pressure Calorimetry

Constant-Pressure Calorimetry uses a coffee cup calorimeter to determine the heat transfers occurring in a liquid solution.

Constant-Volume Calorimetry uses a bomb calorimeter and a combustion reaction to determine its enthalpy of reaction.&nbsp;

First Law of Thermodynamics

The First Law of Thermodynamics states that energy cannot be created nor destroyed, but instead is transferred.&nbsp;

First Law of Thermodynamics -

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