describe how adding thermal energy affects particle motion, temperature, and state.

Short answer: Adding thermal energy increases particle motion, raises temperature, and can drive phase changes; removing thermal energy does the opposite. Details

• Particle motion
  • When thermal energy is added, particles gain kinetic energy and move faster in all states of matter. In gases this appears as more rapid translational motion; in liquids and solids, it shows up as faster translational, rotational, and vibrational motions. The overall effect is a higher average kinetic energy per particle. As energy increases further, particles overcome intermolecular forces more readily, enabling greater displacement and diffusion within the material. [supporting concepts: higher temperature implies greater particle kinetic energy and faster, random motion]

• Temperature
  • Temperature is a measure of the average kinetic energy associated with particle motion in a system. Thus, when thermal energy increases, the average kinetic energy rises and the temperature climbs. Conversely, removing thermal energy lowers the average kinetic energy and lowers the temperature.

• State (phase)
  • Changes in thermal energy can cause phase transitions:
    • Heating a solid typically increases particle motion until the solid’s structure breaks down and it melts into a liquid. Temperature may remain relatively constant during melting because added energy goes into overcoming intermolecular forces rather than increasing kinetic energy, until the phase transition completes.
    • Heating a liquid increases particle motion until it boils into a gas; again, temperature can plateau during the phase change while energy facilitates overcoming cohesive forces.
    • For gases, further heating raises kinetic energy directly, increasing temperature and pressure at fixed volume, or volume at fixed pressure.
  • Cooling (removing energy) reverses these processes: gas condenses to a liquid, liquid freezes to a solid, and solid sublimates or melts depending on conditions. In each case, phase boundaries are reached when energy is allocated to breaking or forming phase-specific interactions rather than changing temperature alone.

Key ideas in one concise model

• Thermal energy is the total energy associated with microscopic motion and interactions.
• Temperature reflects the average kinetic energy of particles (random motion).
• Adding energy raises kinetic energy, increasing motion and temperature; at phase boundaries, added energy can fuel a state change rather than raise temperature.
• Removing energy lowers kinetic energy, reducing motion and temperature; at phase boundaries, energy removal drives phase changes.

If you want, I can tailor this to a specific substance (e.g., water) and walk through the exact energy changes and temperatures at each phase transition.