Boyle's Law: Unraveling the Pressure-Volume Relationship for NEET Chemistry

Introduction

Gas laws are fundamental principles that describe the behavior of gases under varying conditions. Among these, Boyle's Law is a cornerstone, explaining how the volume of a gas changes with pressure. For NEET aspirants, a clear understanding of Boyle's Law is crucial for tackling questions in States of Matter. Let's dive into this essential gas law!

Core Concept

Boyle's Law states that for a fixed amount (moles, n) of an ideal gas at constant temperature (T), the pressure (P) of the gas is inversely proportional to its volume (V).

• Mathematical Expression:
  • P ∝ 1/V (at constant n, T)
  • PV = k (where k is a constant)
  • For two different states of the same gas under constant temperature and moles: P₁V₁ = P₂V₂
• Key Conditions:
  • Constant Temperature (Isothermal Process): The temperature of the gas must not change.
  • Fixed Amount of Gas: The number of moles of gas must remain constant.
• Graphical Representations:
  • P vs. V: A hyperbola (as P increases, V decreases). These curves are called isotherms.
  • P vs. 1/V: A straight line passing through the origin (as P increases, 1/V increases proportionally).
  • PV vs. P (or V): A straight line parallel to the P (or V) axis, indicating that the product PV remains constant.

Solved Example

A gas occupies 2.0 L at 1.5 atm pressure. What will be its volume if the pressure is increased to 3.0 atm at constant temperature?

• Given: P₁ = 1.5 atm, V₁ = 2.0 L, P₂ = 3.0 atm
• To find: V₂
• Formula: P₁V₁ = P₂V₂
• Solution:
  • (1.5 atm) * (2.0 L) = (3.0 atm) * V₂
  • 3.0 atm·L = (3.0 atm) * V₂
  • V₂ = 3.0 atm·L / 3.0 atm = 1.0 L
• Answer: The new volume will be 1.0 L.

NEET Trick

Remember the "Inverse Icon": Imagine two opposing arrows – one going up (Pressure increasing), the other going down (Volume decreasing). This visual helps reinforce the inverse relationship instantly. Always double-check if temperature and the number of moles are stated as constant before applying P₁V₁ = P₂V₂.

Quick Recap

• Boyle's Law: P ∝ 1/V (constant T, n).
• Formula: P₁V₁ = P₂V₂.
• Graphs: P vs V (hyperbola), P vs 1/V (straight line through origin), PV vs P (horizontal line).
• Conditions: Constant temperature and number of moles.
• Application: Used to calculate changes in pressure or volume for ideal gases.