मराठी

Analysis of Observation>From Point B to D

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Topics

Estimated time: 8 minutes
  • Introduction
  • Definition: Vaporisation
  • Definition: Condensation
  • Definition: Boiling Point
  • Real-Life Examples
Maharashtra State Board: Class 11

Introduction

The heating curve is a graph of temperature versus heat energy supplied (or time, if heat is supplied at a constant rate). It shows how water's temperature changes — and pauses — as it transitions through its three states: solid, liquid, and gas.

Heating Curve of Water — Temperature vs Heat Energy diagram showing points A through E, with melting and boiling plateaus

Fig.: Heating Curve of Water: Temperature vs Heat Energy Supplied. The flat plateaus at 0°C and 100°C represent phase changes.

C → D: Liquid Water Heating

Once all the ice has completely melted into water at point B (0°C), and we continue supplying heat, the water's temperature begins to rise steadily. This rise continues from point C (which represents the same water now free of ice) towards point D.

During this stage, the heat energy increases the kinetic energy of water molecules, causing them to move faster. This shows up as a temperature rise on the thermometer.

Maharashtra State Board: Class 11

Definition: Vaporisation

It occurs when a liquid absorbs enough heat energy at its boiling point. The molecules gain enough energy to overcome intermolecular forces and escape into the gas phase.

liquid → vapour (gas)

Maharashtra State Board: Class 11

Definition: Condensation

It occurs when vapour loses heat energy. The molecules slow down enough for intermolecular forces to pull them back together.

vapour (gas) → liquid

Maharashtra State Board: Class 11

Definition: Boiling Point

The temperature at which the liquid and vapour states of a substance coexist in thermal equilibrium. At this temperature, the vapour pressure of the liquid equals the external atmospheric pressure. Adding more heat converts liquid into vapour without raising the temperature.

Maharashtra State Board: Class 11

Real-Life Examples

  • Steam vs Boiling Water Burns: Steam burns are more severe because steam releases extra heat when it condenses.
  • Pressure Cooker: A pressure cooker increases pressure, raising the boiling point of water, so food cooks faster.
  • Cooking at High Altitudes: Low air pressure makes water boil at a lower temperature, so food cooks more slowly.
  • Foggy Mirror: Warm water vapour condenses on a cold mirror, forming tiny droplets.
  • Sweating: Sweat evaporates and absorbs heat, cooling the body.
  • Water Cycle: Water evaporates, condenses into clouds, and falls as rain.

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