Problem 151 - A Complete Resource Book in Chemistry for JEE Main

Question

A pressure cooker reduces cooking time for food because (a) heat is more evenly distributed in the cooking space (b) boiling point of water involved in cooking is increased (c) the higher pressure inside the cooker crushes the food material (d) cooking involves chemical changes helped by a rise in temperature

Step-by-Step Solution

Answer

(b) Boiling point of water involved in cooking is increased.

Step 1: Understanding the Problem

Let's first understand the question. A pressure cooker is known to reduce cooking time. We need to understand the reason behind this by evaluating each given option. This involves knowing the principle behind how a pressure cooker works, specifically related to how it affects the boiling point of water and cooking time.

Step 2: Option Analysis (a)

Option (a) suggests that heat is more evenly distributed in the cooking space. While it's true that pressure cookers can distribute heat well, it's not the primary reason for the reduction in cooking time. Thus, this can be eliminated as the main reason.

Step 3: Option Analysis (b)

Option (b) states that the boiling point of water involved in cooking is increased. This is an important factor because increasing the pressure inside the cooker raises the boiling point of water, allowing the food to cook at a higher temperature than it would at normal atmospheric pressure, thereby cooking food faster. This option seems highly relevant.

Step 4: Option Analysis (c)

Option (c) suggests that higher pressure crushes the food material. While pressure is higher, it does not crush food but rather allows it to cook faster due to the higher boiling point of water.

Step 5: Option Analysis (d)

Option (d) claims that cooking involves chemical changes helped by a rise in temperature. While cooking involves chemical changes, the main function of the pressure cooker in reducing cooking time is linked to the temperature and pressure changes, not directly facilitating chemical reactions.

Step 6: Conclusion and Selection

Having analyzed all options, the primary reason pressure cookers reduce cooking time is because they increase the boiling point of water, thereby allowing food to cook faster. Therefore, option (b) is the correct answer.

Key Concepts

Boiling Point

The concept of boiling point is essential in understanding how a pressure cooker works. The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure surrounding the liquid. For water at sea level, this temperature is 100°C (212°F). However, when you increase the external pressure, as happens inside a pressure cooker, the boiling point of water rises. This means that water can remain in its liquid state at higher temperatures than it would under normal atmospheric conditions. This higher temperature allows food to cook more quickly. It's not just about hitting the boiling point; it's about surpassing it due to the increased pressure, hence why a pressure cooker is so much more efficient.

• At standard atmospheric pressure: Water boils at 100°C
• Under pressure in a cooker: Water boils at a higher temperature

This principle is crucial because by cooking at a higher boiling point, foods can cook faster and more thoroughly, this directly affects the overall cooking time.

Pressure Cookers

Pressure cookers are ingenious devices that utilize the principles of physics to enhance the cooking process. These sealed pots introduce a high-pressured environment, which is quite different from regular cooking methods. By trapping steam, they increase the pressure inside the cooker. This increased pressure raises the boiling point of water, allowing food to be cooked at higher temperatures than normal. The beauty of this system lies in its simplicity. Once sealed, the cooker maintains an airtight environment, which means it only requires a small amount of additional heat to keep the pressure and temperature high.

• Sealed environment: Prevents loss of heat and exchange with outside air
• Increased internal pressure: Raises boiling point and cooking temperature
• Simple operation: Heat is retained efficiently within the cooker

By understanding this process, one can see why pressure cookers are such a valuable tool for reducing cooking times and preparing meals more quickly.

Cooking Time Reduction

Reducing cooking time is one of the standout benefits of using a pressure cooker. With traditional cooking, much of the heat escapes into the surrounding air. In contrast, the pressure cooker locks this heat in, using it efficiently on the food. Because the cooker increases the boiling point of water, food can be cooked at a higher temperature than it would in a regular pot. This results in faster cooking times, which is particularly beneficial for dishes that typically require long cooking durations, such as stews or tough cuts of meat. The time reduction can often be quite substantial, cutting cooking times by more than half in many instances, while still ensuring that the food is cooked evenly and thoroughly.

• Higher cooking temperature: Because of increased boiling point
• Less energy and time required: Heat is used more efficiently
• Effective for tough or long-cook foods: Such as beans or tough meats

By significantly reducing cooking times, pressure cookers make meal preparation quicker, saving both time and energy, without sacrificing the quality of the final dish.