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Worksheet Grade 7 Science

Phase Changes at Stourton Reservoir: A Grade 7 Water-Cycle Worksheet

A grade 7 worksheet using a reservoir through the seasons to model how heat changes particle motion during freezing, melting, and evaporation in the water cycle.

Objectives

  1. Students will describe how particle motion changes when heat is added or removed.
  2. Students will name the state changes water goes through in the reservoir.
  3. Students will connect these state changes to the water cycle.

Vocabulary

Evaporation
Evaporation happens when liquid water, often warmed by the sun, turns into an invisible gas called water vapor that rises into the air. It is how water leaves oceans, lakes, and puddles.
Condensation
Condensation is when water vapor in the air cools down and turns back into tiny liquid water droplets. It is how clouds form and why a cold glass gets wet on the outside on a warm day.

Also: state change, thermal energy, particle

Teacher overview

Water changes state as it moves through the water cycle, and every one of those changes is really a change in how the water particles move. When heat is added, the particles speed up; when heat is removed, they slow down. This worksheet follows the water of one reservoir through a year and asks students to model the particle motion behind freezing, melting, evaporation, and condensation, then tie those changes back to the water cycle.

Phase Changes at Stourton Reservoir: A Grade 7 Water-Cycle Worksheet — Grade 7 Science
Name: ____________________________ Date: ______________

Student Worksheet

Stourton Reservoir is a fictional lake. Use what you know about water particles and state changes to answer the questions.

  1. In winter, the top of Stourton Reservoir freezes into ice. How do the water particles move in ice?
  2. Spring warms the ice. As heat is added, what happens to the motion of the particles?
  3. On a hot day, water evaporates from the surface of the reservoir. What state change is this?
  4. Which has faster-moving particles: the liquid water in the reservoir, or the water vapor above it?
  5. Water vapor rises, cools, and forms a cloud. What is this state change called?
  6. The sun and gravity both drive the water cycle. Which one lifts water into the air?
  7. Water can spend about 9 days in the air before it falls again as rain. Does adding heat make water evaporate faster or slower?
  8. When water freezes, is heat being added to the water or taken away from it?
  9. Describe how the spacing of the particles changes as water goes from a solid to a liquid to a gas.
  10. Explain how the freezing, melting, and evaporating at Stourton are the same changes that move water through the whole water cycle.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: They stay in fixed spots and only vibrate in place.
    In ice, the particles are locked into a set pattern. They still shake a little, but they do not move past one another the way liquid particles do.
  2. Answer: The particles gain energy and move faster.
    As heat is added, the particles speed up until the fixed pattern breaks and the ice melts into liquid water.
  3. Answer: Evaporation (liquid to gas).
    The surface particles gain enough energy to leave the liquid and spread out into the air as water vapor.
  4. Answer: The water vapor.
    A gas has faster-moving particles with more energy than the same substance as a liquid.
  5. Answer: Condensation.
    As the vapor cools, the particles lose energy and slow down, coming close enough together to form liquid droplets in the cloud.
  6. Answer: The sun.
    The sun's energy heats the water and drives evaporation, lifting water into the air. Gravity is what pulls rain and rivers back down.
  7. Answer: Faster.
    Adding heat gives the surface particles more energy, so more of them escape as vapor and the water evaporates faster.
  8. Answer: Taken away.
    Freezing removes heat from the water, so the particles slow down until they lock into the solid pattern of ice.
  9. Answer: The particles move from tightly packed to far apart.
    In a solid they are close together in a fixed pattern; in a liquid they are still close but can slide past one another; in a gas they are far apart and moving fast.
  10. Answer: They are the same state changes that carry water between the ground, the air, and back again.
    Accept answers explaining that melting, evaporation, condensation, and freezing move water from the reservoir into the air and back to the surface, which is the water cycle.

Differentiation

Support

Provide a three-box particle diagram (solid, liquid, gas) with dots already drawn so students can point to the correct box when answering items 1, 4, and 9. Give a word bank with "evaporation," "condensation," "melting," and "freezing."

Extension

Ask students to add one more question of their own about a state change at the reservoir, write a clear answer, and label the particle motion involved.

ELL supports

Pair each vocabulary word with a gesture: fingers still and tight for solid, hands sliding for liquid, hands spread wide for gas. Allow students to draw particle diagrams in place of written sentences for items 1, 2, and 9.