Question

Which of the following statement is false? (1) Thermochemistry is the study of relationship between the heat energy and chemical energy. (2) An exothermic reaction is one which is accompanied by evolution of heat. (3) An endothermic reaction is one in whieh heat is absorbed. (4) The unit that represents largest amount of energy is electron volt.

Short answer

Statement (4) is false.

Step-by-step solution

Understand Thermochemistry

Thermochemistry is indeed the study of the relationship between heat energy and chemical energy. This statement is true.

Define Exothermic Reactions

An exothermic reaction releases heat energy to its surroundings. This statement is true.

Define Endothermic Reactions

An endothermic reaction absorbs heat energy from its surroundings. This statement is true.

Compare Units of Energy

Electron volt (eV) is a unit of energy, but it's not the largest unit of energy. Larger units include the joule (J) and the calorie (cal). Thus, this statement is false.

Key concepts

Exothermic Reactions

Exothermic reactions are chemical processes that release energy in the form of heat. When these reactions occur, the temperature of the surrounding environment increases. This is because the energy stored in the chemical bonds of the reactants is released during the formation of the product bonds. Common examples of exothermic reactions include combustion, such as burning wood, and many oxidation reactions, like iron rusting.

• Heat is released to the surroundings.
• Temperature of the surroundings increases.
• Examples: Burning wood, rusting iron.

Exothermic reactions are crucial in everyday life. They are used in heating applications and play a vital role in various industrial processes. Understanding these reactions helps us utilize their energy efficiently and safely.

Endothermic Reactions

Endothermic reactions absorb heat from their surroundings. This means that the environment around these reactions gets cooler. It occurs because the products of the reaction contain more energy than the reactants, and this additional energy is absorbed from the surroundings. Examples of endothermic reactions include photosynthesis in plants and the cold packs used in sports injuries.

• Heat is absorbed from the surroundings.
• Temperature of the surroundings decreases.
• Examples: Photosynthesis, instant cold packs.

Endothermic reactions are essential in various natural and technological processes. By understanding them, we can harness or manage their cooling effects in practical applications.

Units of Energy

Energy can be measured in various units, some of which are more convenient for different contexts. The Electron Volt (eV) is a unit used in physics, particularly in atomic and particle physics, but it represents a relatively small amount of energy.
The Joule (J) is the standard unit of energy in the International System of Units (SI). It's used extensively in many scientific and engineering fields.
The Calorie (cal), often used in nutrition, is another unit of energy. One calorie is the amount of energy needed to raise the temperature of one gram of water by one degree Celsius.

• Electron Volt (eV) - used in atomic and particle physics.
• Joule (J) - standard SI unit of energy.
• Calorie (cal) - used in nutrition, related to heat energy.

Understanding these units and their applications helps in clearly communicating and calculating energy in various scientific and practical tasks.