Question

The apparatus used for measuring heat of reaction at constant volume is called (a) calorimeter (b) colourimeter (c) pyrometer (d) pyknometer

Short answer

The correct answer is (a) calorimeter.

Step-by-step solution

Identify the purpose of the apparatus

Understand the purpose of the apparatus that is being asked in the question. Here, it is to measure the heat of reaction at constant volume. This hints towards a calorimeter which is commonly used in such experiments.

Compare with the options

Next, compare this understanding with the available options. A colourimeter is used for measuring the intensity of colours, a pyrometer is used to measure high temperatures, and a pyknometer is used to measure the density or specific gravity of liquids. None of these fit the requirement.

Select the answer

After comparing, it can be concluded that a calorimeter is the correct apparatus as it measures the change in heat during a chemical reaction at constant volume.

Key concepts

Heat of Reaction

When substances undergo a chemical reaction, they typically release or absorb a certain amount of heat. This heat exchange is what we refer to as the "heat of reaction." The heat of reaction depends on the conditions under which the reaction takes place – such as temperature and pressure.
The heat of reaction is a crucial concept in chemistry, as it tells us whether a reaction will release energy to the surroundings (exothermic) or absorb energy from them (endothermic).

• An exothermic reaction releases heat, making the surroundings warmer.
• An endothermic reaction absorbs heat, leading to a decrease in temperature.

To quantify this heat change, experiments are conducted under defined conditions, often using a calorimeter to accurately measure the heat released or absorbed. Understanding the heat of reaction helps chemists predict the conditions needed for a reaction and the energy change involved.

Constant Volume

Experiments measuring the heat of reaction are sometimes performed under constant volume conditions. In such setups, the volume of the system doesn't change, which simplifies calculations.
By keeping volume constant, chemists can focus on the heat effects alone without interference from changes in pressure or volume. An ideal tool for these kinds of measurements is the bomb calorimeter, which allows reactions to occur in a sealed container.

• Since no work is done by expanding or compressing the volume, experiments at constant volume directly relate to changes in internal energy.

Using a calorimeter under these conditions ensures that the heat measured corresponds to the internal energy change, which is crucial for accurate thermal analysis.

Chemical Reactions

Chemical reactions are processes where substances, called reactants, transform into different substances, known as products. These transformations involve breaking and forming chemical bonds.
Chemical reactions are everywhere; they power cars, make food digestible, and are even essential for life processes.
When analyzing chemical reactions, scientists categorize them into different types based on the reaction process.

• Synthesis reactions involve combining simpler substances to form something more complex.
• Decomposition reactions break down compounds into simpler parts.
• Combustion reactions, typically involving a reactant and oxygen, rapidly produce heat and light.

Understanding the nature of these reactions allows scientists to harness them effectively in various applications. Knowing the heat exchange in these reactions is crucial, as it helps in designing reactions that are safe, efficient, and energy-conscious.