Problem 2 - A Complete Resource Book in Chemistry for JEE Main

Question

The beans are cooked sooner in a pressure cooker, because (a) boiling point increase with increasing pressure (b) boiling point decrease with increasing pressure (c) extra pressure of pressure cooker, softens the beans (d) internal energy is not lost while cooking in pressure cooker.

Step-by-Step Solution

Answer

(a) Boiling point increases with increasing pressure.

Step 1: Understanding the Concept

The reason a pressure cooker cooks food faster is primarily physics that relates to pressure and boiling point. When pressure increases, the boiling point of water also increases. This means that water boils at a higher temperature, cooking food more rapidly.

Step 2: Analyzing the Options

Let's look at the options provided: (a) Boiling point increases with increasing pressure. (b) Boiling point decreases with increasing pressure. (c) Extra pressure softens the beans. (d) Internal energy is not lost while cooking. Option (a) is correct, as it reflects the scientific principle that higher pressure increases the boiling point, facilitating faster cooking.

Step 3: Eliminating Incorrect Options

We can eliminate (b) because it incorrectly states that boiling point decreases with pressure. Option (c) focuses on the softening factor, a secondary effect rather than the primary reason. While (d) deals with energy conservation, it does not directly address why cooking is faster in a pressure cooker.

Step 4: Selecting the Correct Answer

Based on the scientific understanding and analysis of the options, option (a) is selected as the correct answer: Boiling point increases with increasing pressure, which helps cook the beans faster.

Key Concepts

Boiling Point

When we talk about the boiling point, we're referring to the temperature at which a liquid turns into vapor. For water, this usually happens at 100°C (212°F) at standard atmospheric pressure. However, when you increase pressure, as in a pressure cooker, the boiling point of water becomes higher than in regular atmospheric conditions.

Here's why that's important:

• Increased Temperature: With a higher boiling point, water inside the pressure cooker can reach hotter temperatures.
• More Heat Energy: This means more energy is available to cook food, leading to faster cooking times.

By controlling the pressure, you effectively control the boiling point, harnessing heat energy more efficiently while cooking.

Cooking Faster

The core advantage of a pressure cooker is its ability to cook food faster. This is directly tied to how the pressure cooker uses the physics of pressure and boiling points.

• Higher Temperature: As the boiling point rises, the temperature of steam inside the cooker can exceed typical boiling temperatures.
• Efficient Cooking: Foods are exposed to higher heat, which helps break down complex proteins and fibers more quickly.
• Time-saving: Dishes that might take hours to cook can be completed in a fraction of the time with the same tenderness and flavor.

By increasing the boiling point and keeping steam trapped inside, a pressure cooker vastly speeds up the cooking process.

Pressure Increase Effect

Pressure has a direct impact on cooking dynamics through its effects on boiling point and energy retention. In a pressure cooker, the lid locks airtight, trapping steam and increasing pressure inside the pot.

• Pressure Build-up: As more steam is created than can escape, pressure builds up inside the cooker.
• Temperature Rise: This increased pressure raises the temperature of the boiling water past what you'd achieve through normal means.
• Better Energy Use: Each degree of increased temperature allows for energy to continue cooking the food at a higher rate.

By understanding this, you can see how pressure cookers utilize physical laws to improve cooking efficiency and speed.