Energy bomb calorimeter

Thermochemistry is concerned with the study of thermal effects associated with phase changes, formation of chemical compouncls or solutions, and chemical reactions in general. The amount of heat (Q) liberated (or absorbed) is usually measured either in a batch-type bomb calorimeter at fixed volume or in a steady-flow calorimeter at constant pressure. Under these operating conditions, Q= Q, = AU (net change in the internal energy of the system) for the bomb calorimeter, while Q Qp = AH (net change in the enthalpy of the system) for the flow calorimeter. For a pure substance. 

As noted earlier, for a reaction at constant pressure, such as that taking place in an open coffee-cup calorimeter, the heat flow is equal to the change in enthalpy. If a reaction is carried out at constant volume (as is the case in a sealed bomb calorimeter) and there is no mechanical or electrical work involved, no work is done. Under these conditions, with w = 0, the heat flow is equal to the change in energy, AE. Hence we have... 

Acetylene, C2H2, is used in welding torches. It releases a lot of energy when burned in oxygen. One gram of acetylene releases 48.2 kj. When 0.750 g of acetylene is burned in a bomb calorimeter (heat capacity = 1.117 kJ/°C), the final temperature of the bomb is 54.5°C. What is the initial temperature of the calorimeter ... 

FIGURE 6.12 A bomb calorimeter is used to measure heat transfers at constant volume. The sample in the central rigid container called the bomb is ignited electrically with a fuse wire. Once combustion has begun, energy released as heat spreads through the walls of the bomb into the water. The heat released is proportional to the temperature change of the entire assembly. 

We have seen that a constant-pressure calorimeter and a constant-volume bomb calorimeter measure changes in different state functions at constant volume, the heat transfer is interpreted as A U at constant pressure, it is interpreted as AH. However, it is sometimes necessary to convert the measured value of AU into AH. For example, it is easy to measure the heat released by the combustion of glucose in a bomb calorimeter, but to use that information in assessing energy changes in metabolism, which take place at constant pressure, we need the enthalpy of reaction. 

Figure 3.6 Schematic representation of the bomb calorimeter for measuring the changes in internal energy that occur during combustion. The whole apparatus approximates to an adiabatic chamber, so we enclose it within a vacuum jacket (like a Dewar flask)...

Worked Example 3.5 A sample of glucose (10.58 g) is burnt completely in a bomb calorimeter. What is the change in internal energy A U if the temperature rises by 1.224 K The same heater as that in SAQ 3.3 is operated for 11240 s to achieve a rise in temperature of 1.00 K. 

SAQ 3.4 A sample of anthracene (C14H10, II) was burnt in a bomb calorimeter. A voltage of 10 V and a current of 1.2 A were passed for exactly 15 min to achieve the same rise in temperature as that caused by the burning of 0.40 g. Calculate the molar energy liberated by the anthracene. 

Propane gas, C3H8, is sometimes used as a fuel. In order to measure its energy output as a fuel a 1.860 g sample was combined with an excess of 02 and ignited in a bomb calorimeter. After the reaction, it was found that the temperature of the calorimeter had increased from 25.000°C to 26.061°C. The calorimeter contained 1.000 kg of water. The heat capacity of the calorimeter was 4.643 kJ/°C. Determine the heat of reaction, in kJ/mol propane. The reaction was ... 

Most static-bomb calorimeters used are of the isoperibol type, such as the one in figure 7.1. Here, the bomb A is a pressure vessel of 300 cm3 internal volume. Combustion bombs are usually made of stainless steel and frequently have an internal platinum lining to prevent corrosion. In a typical high-precision experiment, the platinum ignition wire B connects the two electrodes C, which are affixed to the bomb head. A cotton thread fuse D (other materials such as polyethene are also used), of known energy of combustion, is weighed to a precision of 10-5 — 10-6 g and tied to the platinum wire. A pellet E of the compound... 

Alternatively, the combustion of a certified reference material can be used. Since 1934, benzoic acid has been the internationally accepted primary standard material for determination of the energy equivalent of oxygen-bomb calorimeters [39,40]. In this case,... 

In your previous chemistry course, you learned about various types of calorimeters. For instance, you learned about a bomb calorimeter, which allows chemists to determine energy changes under conditions of constant volume. 

The energy in food is in the form of carbohydrate, fat and protein, and the oxidation of these compounds, in vitro, transfers the chemical energy into heat which can then be measured. This is done in what is known as a bomb calorimeter (Figure 2.1). The heat released in the calorimeter when 1 g of carbohydrate, fat, protein or other fuel is fully oxidised (i.e. Af/) is given in Table 2.3. 

Gross calorific value (gross heat of combustion at constant volume) heat produced by combustion of a unit quantity of a solid or liquid fuel when burned at constant volume in an oxygen bomb calorimeter under specified conditions, with the resulting water condensed to a liquid not applied to gaseous fuels and applies to a volatile liquid fuel only if it is suitably contained during the measurement closely related to the internal energy of combustion for the same reaction at constant standard temperature and pressure. 

In a constant-volume bomb calorimeter with a heat capacity of 13.418 kJ/K, 1.17 g of naphthalene, C10H8, is burned. Fifty-two joules of energy are required to ignite the sample. If the temperature rise of the calorimeter is 3.318 K, what is the A U and AH of combustion of naphthalene What is the AHy of naphthalene (You may assume that all water is formed in the liquid phase.)... 

Chemists always need to know bond energies, often for unusual combinations of elements, for which bomb combustion calorimetry experiments have never been done, partly because the appetite of conventional bomb combustion calorimeters for large samples is not easily met for rare compounds. Thus there is a need for future micro rotating-bomb calorimeters. 

The heat of combustion is the amount of heat released when a compound is burned with an excess of oxygen in a sealed container called a bomb calorimeter. If the compound has extra energy as a result of ring strain, that extra energy is released in the combustion. The heat of combustion is usually measured by the temperature rise in the water bath surrounding the bomb. ... 

The heat given off when a mole of a compound is burned with excess oxygen to give C02 and H20 in a bomb calorimeter. A measure of the energy content of a molecule, (p. 110)... 

It works on the same general principle as the polystyrene calorimeter. The reaction, however, takes place inside an inner metal chamber, called a bomb. This bomb contains pure oxygen. The reactants are ignited using an electric coil. A known quantity of water surrounds the bomb and absorbs the energy that is released by the reaction. You will learn more about bomb calorimeters later in this section. 

By comparing the thermal energy that is released when fats, proteins, and carbohydrates are burned in a bomb calorimeter, you can compare the energy that is stored in these compounds. Natural fats are made up of various types of fatty acids. Fatty acids are long chain organic acids. The most common fatty acid in nature is oleic acid. 

A substance is burned completely in a bomb calorimeter. The temperature of the 2000 g of water in the calorimeter rises from 25.0 ,C to 43.9°C. How much energy is released ... 

---