Question

Describe a combustion calorimeter. What information can it give?

Short answer

A combustion calorimeter measures the heat released during combustion, providing the enthalpy of combustion. This information helps in determining fuel efficiency and energy content.

Step-by-step solution

Introduction to Combustion Calorimeter

A combustion calorimeter is a device used to measure the amount of heat released during a combustion reaction. The heat is referred to as the enthalpy of combustion.

Design of a Combustion Calorimeter

The calorimeter typically consists of a strong, insulated container that holds the sample to be combusted. It often includes a bomb, which is a sealed container where the combustion reaction occurs, filled with oxygen to ensure complete combustion.

Working of a Combustion Calorimeter

The sample is ignited electrically, and the heat produced by the combustion is absorbed by a known quantity of water surrounding the bomb. The temperature change in the water is measured accurately.

Energy Measurement

By knowing the mass of the sample, the specific heat capacity of the water, and the temperature change, the amount of heat released during the combustion can be calculated using the formula: \[ q = m \times c \times \triangle T \] where \( q \) is the heat absorbed, \( m \) is the mass of the water, \( c \) is the specific heat capacity of water, and \( \triangle T \) is the change in temperature.

Information Provided

The calorimeter provides the enthalpy of combustion, which can be used to determine the energy content of fuels, compare different fuels' efficiencies, and understand various thermodynamic properties of substances.

Key concepts

enthalpy of combustion

The enthalpy of combustion, also known as the heat of combustion, is the heat released when a substance undergoes complete combustion with oxygen under standard conditions. This concept is vital in understanding the energy content of different fuels. It is measured using a combustion calorimeter by determining the temperature change of a known quantity of water.
The formula used to calculate the enthalpy of combustion is:
\[ \Delta H_{comb} = - q = - m \times c \times \Delta T \]
Here, the negative sign indicates that heat is released by the system. Enthalpy of combustion is expressed in units of energy per mole, such as kJ/mol. By knowing this value, we can compare the efficiencies of different fuels and make informed decisions concerning energy sources.

specific heat capacity

Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. It is a crucial property in calorimetry, as it helps in calculating the heat absorbed or released by a substance. For water, the specific heat capacity is typically taken as 4.18 J/g°C.
Knowing the specific heat capacity allows us to use the formula \[ q = m \times c \times \Delta T \] to find the heat absorbed or released during combustion. In this equation:

• \(q\): Heat absorbed or released (in joules)
• \(m\): Mass of the water (in grams)
• \(c\): Specific heat capacity (in J/g°C)
• \(\Delta T\): Change in temperature (in °C)

This property also helps in understanding and comparing different materials' thermal behaviors, an essential aspect of thermodynamics.

calorimetry

Calorimetry is the science of measuring the heat of chemical reactions or physical changes. A combustion calorimeter is an example of a device used in calorimetry. In such a device, the substance is burned in a bomb calorimeter, and the heat released during combustion is absorbed by the surrounding water, increasing its temperature.
To measure this heat change accurately:

• The calorimeter must be well-insulated to prevent heat loss to the environment.
• The amount of water and its initial temperature must be accurately known.
• The sample must undergo complete combustion.

The data obtained from calorimetry helps determine various thermodynamic properties, including the enthalpy changes of substances during reactions. It is a foundational technique in thermochemistry and plays a significant role in energy analysis.

thermodynamic properties

Thermodynamic properties are characteristics of a system that can be quantified and used to understand the system's energetic behavior. These properties include enthalpy, entropy, and specific heat capacity.

• Enthalpy (\(H\)): A measure of the total energy of a thermodynamic system, often associated with the heat content in a constant-pressure process, like combustion.
• Entropy (\(S\)): Represents the disorder or randomness in the system, which tends to increase during combustion due to the irreversible nature of the process.
• Specific Heat Capacity (\(c\)): As covered earlier, it is crucial in calorimetric calculations to determine the heat exchanged in reaction.

These properties are interconnected and essential in describing the energy changes and the efficiency of reactions. By understanding them, we can better grasp how energy is converted, transferred, and conserved in chemical processes, like the combustion measured in a calorimeter.