States of Matter

Easy

1. Multiple Choice: Which of the following substances is a solid?
   A. Air
   B. Ice cube
   C. Rainwater
   Answer: B
   Explanation: Air is a gas, rainwater is a liquid, and an ice cube is frozen water in a solid state with a fixed shape and volume.
2. Fill in the Blank: The phase change of water turning into ice is called ______.
   Answer: freezing
   Explanation: Freezing is the process where a liquid changes into a solid by releasing heat, which matches the change of liquid water to solid ice.

Medium

1. Short Answer: Explain why wet clothes dry faster in summer than in winter (analyze from the perspective of particle motion).
   Answer: The evaporation of water on wet clothes is a form of vaporization, which depends on the motion speed of water molecules. Summer has a higher temperature, so water molecules move more vigorously. More molecules can overcome interparticle forces and escape from the liquid surface into the air, making the clothes dry faster.
   Explanation: The key is to link temperature, particle motion speed, and the vaporization process. Higher temperature increases particle kinetic energy, accelerating evaporation.
2. True/False: A substance absorbs heat when changing from a gas to a solid. (√/×)
   Answer: ×Explanation: The phase change from gas to solid is deposition, which releases heat. Heat absorption occurs in endothermic processes like melting, vaporization, and sublimation.

Hard

1. Analysis: Why can increasing pressure cause a gas to liquefy? (Explain from the perspective of particle distance and interparticle forces)
   Answer: Gases have large distances between particles and weak interparticle forces. When pressure is increased, the space between gas particles is compressed, reducing their distance. As the distance decreases, the interparticle forces become strong enough to hold the particles together, converting the gas into a liquid with a fixed volume.
   Explanation: The analysis must connect pressure, particle distance, and interparticle forces. Increased pressure reduces particle separation, enhancing intermolecular attractions to trigger condensation.
2. Experimental Design: Design an experiment to prove that "heat absorption is required for a solid to melt". List the experimental materials, procedures, and phenomena.
   Answer:
   • Materials: Ice cubes, beaker, thermometer, insulating foam, hot water.
   • Procedures:
     1. Place ice cubes in a beaker and insert a thermometer to record the initial temperature (0°C for pure ice).
     2. Place the beaker in a larger container of hot water and wrap the gap with insulating foam to ensure slow, uniform heating.
     3. Continuously observe the thermometer reading and the state of the ice during heating.
   • Phenomena: The thermometer remains at 0°C until all the ice melts into water. After melting, the temperature of the water starts to rise.
   • Conclusion: During the melting of ice, heat is absorbed from the hot water, but the temperature does not increase. This proves that solid melting requires heat absorption.
      
     Explanation: The constant temperature during melting is a key evidence of heat absorption for phase change, rather than temperature increase. The insulating foam prevents heat loss, ensuring the validity of the experiment.