Melting point - Definition, Examples, Facts & Quiz, FAQ, Trivia
Discover how solids transform into liquids at specific temperatures
What is Melting Point?
Melting point is the specific temperature at which a solid turns into a liquid. This happens because the molecules gain enough energy to break free from their fixed positions and start moving around.
Key facts about melting point:
• Every solid has its own melting point
• For pure water ice, melting point is 0°C (32°F)
• Melting is a physical change, not chemical
• Adding substances to a solid can change its melting point
Think of melting point like a special temperature doorway. When the temperature rises above this doorway, solids walk through and become liquids!
Key Concept
Melting point is the temperature where a substance changes from solid to liquid. This change happens because molecules gain energy and break free from their fixed positions.
Solid state
(Ice cube)
Phase change occurs
(Ice ↔ Water)
Liquid state
(Water flows)
Solids & Melting
Not all solids melt the same way! There are two main types of solids:
Crystalline Solids:
• Have a regular, repeating pattern of molecules
• Examples: Salt, sugar, diamonds, ice
• Melt at a specific, sharp temperature
Amorphous Solids:
• Have molecules arranged randomly
• Examples: Glass, plastic, rubber
• Soften gradually over a range of temperatures
Crystalline solids have a definite melting point because their molecules are arranged in a specific pattern. Amorphous solids don't have a sharp melting point because their molecules aren't organized.
Crystalline Solids
Orderly molecular structure
Sharp melting point
Amorphous Solids
Random molecular arrangement
Softens gradually
Glass Transition
Amorphous solids like glass don't melt suddenly. Instead, they go through a "glass transition" where they gradually soften as they heat up, becoming more flexible before finally melting.
Melting Point of Water
Pure water ice melts at exactly 0°C (32°F) at sea level. But this temperature can change depending on:
Factors affecting ice's melting point:
• Impurities: Adding salt lowers melting point
• Pressure: Higher pressure lowers melting point slightly
• Size: Smaller ice crystals melt faster
• Air pressure: Lower air pressure lowers melting point
Did you know that ice is less dense than liquid water? That's why ice floats in water! This unusual property is very important for life on Earth.
Solid Ice
Below 0°C (32°F)
Molecules in fixed positions
Liquid Water
Above 0°C (32°F)
Molecules flow freely
Pressure Melting
Under high pressure, ice can melt at temperatures below 0°C. This is why ice skates glide so smoothly - the pressure from the blade melts the ice just beneath it, creating a thin layer of water!
Changing Melting Point
Several factors can change a substance's melting point:
Impurities:
• Adding other substances usually lowers melting point
• Salt on icy roads causes ice to melt below 0°C
• This is called melting point depression
Pressure:
• For most substances, higher pressure increases melting point
• But for water, higher pressure lowers melting point
• This is why glaciers can flow - pressure melts ice at their base
Size:
• Smaller particles melt at lower temperatures
• This is why snow melts faster than large ice cubes
Impurities
Adding salt to ice lowers its melting point to about -9°C (15°F)
Pressure
High pressure lowers water's melting point but raises it for most other substances
Size
Small ice crystals melt faster than large blocks of ice
Crystalline Structure
Stronger molecular bonds mean higher melting points
Melting Point Quiz
Test your knowledge of melting point with this 5-question quiz. Choose the correct answer for each question.
Frequently Asked Questions
Here are answers to common questions about melting point:
Science Trivia
Discover amazing facts about melting point:
Highest Melting Point
Tungsten has the highest melting point of all metals at 3422°C (6192°F)! It's used in light bulb filaments and rocket engine nozzles.
Lowest Melting Point
Helium has the lowest melting point at -272.2°C (-458°F)! At normal pressures, it remains liquid all the way down to absolute zero.
Hand-Melting Metal
Gallium melts at just 29.8°C (85.6°F), which is below body temperature. A gallium spoon will melt in a cup of hot tea!
Diamond's Secret
Diamonds melt at about 4027°C (7280°F) - that's hotter than the surface of the sun! But in normal air, they burn before melting.
