Thermal Energy — Important Questions

Gases

Gases show the maximum thermal expansion among all states of matter. Step 1: In solids, atoms are tightly bound and can only vibrate slightly, leading to small expansion. Step 2: In liquids, molecules are less tightly bound than solids, allowing moderate expansion. Step 3: In gases, molecules are widely spaced and move freely, allowing maximum expansion when heated. Step 4: The expansion follows the order: gases > liquids > solids. Step 5: This is why gas thermometers are very sensitive to temperature changes.

0°C

Pure water melts (ice melts) at 0°C under standard atmospheric pressure. Step 1: The melting point is the temperature at which a solid changes to liquid state. Step 2: For pure water, this occurs at exactly 0°C (or 32°F or 273 K). Step 3: This is used as the lower fixed point in the Celsius temperature scale. Step 4: At this temperature, ice and water can coexist in equilibrium. Step 5: 100°C is the boiling point, not melting point, while 32°C and 273°C are incorrect values.

It remains constant

During melting, the temperature remains constant even though heat is being supplied. Step 1: When a solid reaches its melting point, additional heat energy doesn't increase temperature. Step 2: Instead, this heat energy (called latent heat of fusion) breaks the bonds holding the solid structure together. Step 3: The energy is used to overcome intermolecular forces, not to increase kinetic energy of molecules. Step 4: Only after complete melting does further heating increase temperature again. Step 5: This constant temperature during phase change is a characteristic property of pure substances.

Water

Water has a much higher specific heat capacity than copper. Step 1: Water's specific heat capacity is 4200 J/kg/K, while copper's is only 380 J/kg/K. Step 2: This means water requires about 11 times more energy than copper to raise the same mass by 1°C. Step 3: Water's high specific heat is due to hydrogen bonding between molecules, which requires extra energy to break. Step 4: This property makes water excellent for cooling systems and climate moderation near large water bodies. Step 5: Metals like copper generally have lower specific heat capacities than water.