Problem 38 - A Complete Resource Book in Chemistry for JEE Main

Question

The amount of heat required to raise the temperature of one mole of the substance through \(1 \mathrm{~K}\) is called, its (a) molar heat (b) entropy (c) thermal capacity (d) specific heat

Step-by-Step Solution

Answer

The term is 'molar heat,' aligning with option (a).

Step 1: Understanding the Question

The problem asks us to identify the term that describes the amount of heat needed to increase the temperature of one mole of a substance by 1 Kelvin. We need to determine which of the provided options fits this definition.

Step 2: Analyzing Each Option

Option (a) 'molar heat' is a vague term and does not specifically define the heat requirement for a mole related to temperature change. Option (b) 'entropy' is a measure of disorder or randomness, not the heat change with temperature. Option (c) 'thermal capacity' refers to the amount of heat needed to raise the temperature of an entire system by 1 degree, not specifically for one mole. Option (d) 'specific heat' generally refers to per unit mass, but combined with the term 'molar,' it relates to one mole of substance.

Step 3: Defining the Correct Term

The term 'molar heat capacity' or simply 'molar heat' when implied in context refers to the heat required to raise one mole of substance by 1 Kelvin. This aligns with option (a) 'molar heat.' However, since this exact terminology (molar heat) in the option should be specified clearly as 'molar heat capacity,' at times, general references may use 'molar heat.' Thus, it matches the context described.

Key Concepts

Thermal Capacity

Thermal capacity, also known as heat capacity, is an important concept in thermodynamics. It describes how much heat is needed to increase the temperature of an entire system by one degree Celsius or Kelvin. Unlike specific heat, which looks at how much heat is needed per unit mass, thermal capacity considers the whole system.

To fully understand thermal capacity, imagine you're heating a pot of water on the stove. The thermal capacity would be the total amount of heat you need to add to the entire pot to raise its temperature by one degree. This includes both the water and the pot itself.

Key points about thermal capacity:

• It applies to the whole system, not just a single component.
• Measurement units are typically in Joules per degree Celsius (J/°C) or Kelvin (J/K).
• The thermal capacity can change when the nature or mass of the system changes.

Understanding thermal capacity is useful in various practical applications, such as designing heating systems for buildings, manufacturing processes, and evaluating energy efficiency.

Specific Heat

Specific heat is another crucial concept in the study of thermodynamics. It refers to the amount of heat required to raise the temperature of one unit mass of a substance by one degree Celsius or Kelvin. This property is unique to each material and affects how it responds to heat.

For example, water has a high specific heat, meaning it requires a lot of heat energy to change its temperature. That's why water is effective in regulating temperature in environments, such as oceans and climate control systems.

Key characteristics of specific heat include:

• Units are generally Joules per gram per degree Celsius (J/g°C) or Joules per kilogram per Kelvin (J/kgK).
• Helps determine how substances change temperature when absorbing or releasing heat.
• Important for cooking, material science, and meteorology, among other fields.

When you know the specific heat of a material, you can predict how it will react in various temperature-changing scenarios, aiding in both scientific and industrial applications.

Heat Transfer

Heat transfer is the movement of thermal energy from one object or system to another due to a temperature difference. There are three main methods of heat transfer: conduction, convection, and radiation.

Conduction is when heat transfers through direct contact between materials. Think of it like a spoon getting hot when placed in a pot of boiling soup. Convection occurs when heat is transferred through fluid movements, such as air or liquid. This is what happens when you feel the warm air blowing out of a heater.

Radiation is heat transfer through electromagnetic waves, such as the warmth you feel from the sun even though there's no direct contact. Each of these methods plays a role in everyday experiences and industrial practices.

Important aspects of heat transfer:

• Relies on temperature differences to occur—heat always moves from a hotter to a cooler place.
• Is fundamental in everything from weather patterns to engineering design.
• Can influence climate, cooking methods, and energy efficiency in buildings.

Understanding heat transfer is critical for designing efficient systems that manage thermal energy effectively, ensuring comfort, and reducing energy consumption.